下列群落的演替类型中，属于初生演替的是               

A．外来物种入侵，改变群落物种组成	B．弃耕农田上长出杂草、灌木
C．在火山岩上长出地衣	D．对砍伐后的森林进行封山育林

下列群落的演替类型中，属于初生演替的是               

A．外来物种入侵，改变群落物种组成	B．弃耕农田上长出杂草、灌木
C．在火山岩上长出地衣	D．对砍伐后的森林进行封山育林

如图所示，甲是探究“动能的大小与什么因素有关”的实验装置,实验中让同一钢球从斜面上不同的高度由静止滚下，碰到同一木块上．乙是探究“阻力对物体运动的影响”的实验装置，实验中让同一小车从斜面上相同的高度由静止滑下，在粗糙程度不同的水平面上运动．请回答下列问题：

　　（1）甲实验的目的是探究钢球动能的大小与             的关系；实验时，它是通过观察            ，从而判断钢球动能的大小。
　　（2）进行乙实验时，每一次都让同一小车从斜面上相同的高度由静止滑下，其目的是使小车在水平面运动的起始             相同；通过观察小车在粗糙程度不同的水平面上运动            来判断小车在不同的水平面受到            的大小．从而可以推理：如果运动的物体不受力，它将                。

Many students in China are learning English. Some of these students are small children. Others are teenagers(青少年). Many are adults(成年人). Some study at school, others learn by themselves. A few learn English language over the radio, on TV, or in the films. One must work hard to learn another language.
Why do all these people want to learn English? It is difficult to answer that question. Many boys and girls learn English at school because it is one of their subjects. They study their own(自己的) language and maths and English. Some people learn English because it is useful for their work. Many people often learn English for their higher studies, because at college or university(大学) some of their books are in English. Other people learn English because they want to read newspapers and magazines in English.
【小题1】根据Others are teenagers(青少年). Many are adults(成年人).描述，可知选C。
【小题2】根据短文第一段描述，可知孩子，年轻人和成人都在学英语。故选C。
【小题3】根据短文第二段描述，可知每个人学英语都有不同的原因，故选D。
【小题4】联系上文可知本文描述的是中国人学英语，故他们自己的语言是汉语，选A。
【小题5】by表示通过某种方式，通过自己学习英语，及自学英语，故选B。
【小题6】Are there many adults learning English in China?

A．No, they aren’t.	B．No, they are.
C．Yes, there are.	D．Yes, there aren’t.

【小题7】________learn English.

A．Only teenagers.

B．Only adults.

C．Small children, teenagers and adults.

D．Only small children.

【小题8】Which of the following is true?

A． Most people learn English over the radio.

B． All the people learn English at school.

C． Students only learn their own language at school.

D． Different people have different reasons for learning English.

【小题9】“Their own language” means_____________.

A．Chinese

B．English

C．French

D．Japanese

【小题10】What’s the Chinese meaning of “learn by themselves”?\

A．和他们一起学习

B．自学

C．向他们学习

D．通过学习