Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.
Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).
Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

【小题1】If the bottom of an object is ______ its top, it will fall over easily.

A．lighter than

B．heavier than

C．no heavier than

D．as heavy as

【小题2】Please point out which box will not fall.

【小题3】The main idea of the passage is _________.

A．why things fall over	B．a low center of gravity
C．a high center of gravity	D．that everything has weight

Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.

Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).

Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

1.If the bottom of an object is ______ its top, it will fall over easily.

A. lighter than　　 B. heavier than　　 C. no heavier than　　  D. as heavy as

2.Please point out which box will not fall.

3.The main idea of the passage is _________.

A. why things fall over　　　　         B. a low center of gravity

C. a high center of gravity　　             D. that everything has weight

 

Choose the object complement in the following sentence

 

I found the story very boring.

A   B　　  C　　　　　　 D

Reading Comprehension

　　A barn owl(猫头鹰) silently flies at night through the dark forest. Suddenly, the large bird hears a mouse running through the leaves. The bird quickly changes its flight path, drops down, and scoops up(抓起) the mouse in its talons(猛禽的爪). Another meal has been successfully captured.

　　How is the barn owl able to pinpoint the location of the mouse in the dark? Credit(把…归功于) the bird' s excellent hearing and its ability to determine the exact location of the source of a sound.

　　According to a recent study at Stanford University, a barn owl learned how to pinpoint the location of a sound source when it was only about two weeks old. The owl did this by noting the difference in the time it took a sound to reach each ear and in the difference in the loudness of the sound in each ear.

　　In another test, three young barn owls were given eyeglasses when their eyes were just beginning to open. The lenses(镜片) in the glasses distorted(使变形) a scene so that an object an owl was looking at seemed to be 20 degrees to the left of its actual position.

　　The scientists found that whenever one of the young owls heard a sound, it would look at a spot 20 degrees to the left of the sound source. Thus, the scientists concluded, the owls learned at a very young age how to locate the source of a sound.

1．What is the reason for the barn owl to successfully catch the mouse?

[　　]

A．It has very good eyesight at night.

B．It has very sharp hearing.

C．It is very good at determining the location of the sound.

D．Both B and C.

2．According to a recent study, a barn owl learned how to ________ when it was only about two weeks old.

[　　]

A．fly fast without sound

B．catch the mouse with its talon

C．locate the sound source

D．open its eyes wider

3．What do the words “to pinpoint the location” in the second paragraph mean?

[　　]

A．To find the exact position.

B．To notice the particular smell.

C．To recognize the real shape.

D．To hear the sound clearly.

4．Why did one of the young owls, after hearing a sound, look at a spot 20 degrees left of the sound source?

[　　]

A．It was too young to find the correct spot.

B．It was used to looking at the spot 20 degrees to the left of an object.

C．It was a mistake often made by this young owl.

D．It was wearing eyeglasses which distorted the object.

5．What is the main idea of the passage?

[　　]

A．How did the scientists train the owls to catch mice at night?

B．Why can eyeglasses help owls to catch mice?

C．Scientists used eyeglasses to make owls see better.

D．Why can owls catch mice at night?

Reading Comprehension

　　A magnet has an attractive force on magnetic substances placed near it. The force is greatest at the poles of the magnet. The force is in the magnet itself. The force is also felt outside the magnet. The region around the magnet in which the magnetic force can be felt by a magnetic substance is called the magnetic field of the magnet. You cannot see a magnetic field but you can see what the force in a magnetic field can do.

　　When a bar magnet is hung freely, it comes to rest in a north-south direction. Another bar magnet hung in the same way, some distance away, will also come to rest in the same direction as the first magnet. The reason the bar magnets come to rest in a north-south direction is because of the Earth's magnetism. There is a very large magnetic field all around the Earth. The magnetic field seems to be produced by a huge magnet in the Earth, with its South Pole pointing towards the north and its North Pole pointing towards the south all the time.

　　The magnetic poles of the Earth are not at the same positions as the geographic poles. They are a short distance away from each other. The small angle between them is called the magnetic declination. The magnetic declination is different at different places on the Earth. It also changes slightly from year to yeas because of the changes in the Earth's magnetic field. Navigators must consider magnetic declination in their calculations.

1．When the magnetic needle of a compass is allowed to move freely, it will come to rest in line with the Earth's ________.

[　　]

2．In paragraph 1, magnet means any object that can ________ and attract small pieces of iron.

[　　]

A．produce a magnetic force

B．form a magnetic field

C．use a magnetic field

D．change magnetic substances

3．The geographic North Pole is ________ the magnetic north pole.

[　　]

A．at the same position of

B．different from

C．at the opposite position of

D．the same as

4．Magnetic compasses are used by travellers and navigators to ________ in which they are travelling.

[　　]

A．indicate the South Pole

B．indicate geographic poles

C．tell them the declination

D．tell them the direction

5．Which of the following statements is true?

[　　]

A．A magnet has an attractive force on every substance placed near it.

B．When a bar magnet is hung freely, it comes to rest in a north-south direction.

C．The magnetic poles of the Earth are at the same positions as the geographic poles.

D．The magnetic declination is same at different places on the Earth.