through, across, over

1. She swam ________ the river.

2. The man jumped ________ the wall and went away.

3. He walked ________ the forest.

since, for

1. I have learned English ________ 1990.

2. I have learned English ________ over 10 years.

________ these words, he left the office in a hurry.

________ the beginning of 21st century, the world's population was over 6 billion.

It will stop the sand ________ moving ________ the rich farmland in the south.

The book is very ________ (interest). Are you ________ (interest) in it?

They couldn't afford ________（买数码摄像机）because it was much too expensive for them.

I ________ (ring) you up as soon as the letter ________ (receive).

So far, many man-made satellites ________ (send) up into space.

Please give me a________（描述）of the scenery of Mount Liang.