In a few years' time, those mountains ________trees.

A. have been covered with

B. are covered by

C. will be covered with

D. will cover by

I believe that those mountains ________ trees in a few years' time.

A. are covered with

B. will be covered with

C. are covering by

D. will cover by

I believe that those mountains ________ with trees in a few years' time.

A. are covered

B. will be covered

C. are coveting

D. will cover

Forests help to keep water from running away，so drought（干旱）doesn’t often happen．Chinese people have built a“Great Wall”of trees，millions of trees across the northern part of the country．

    The Great Green Wall 1 ________ （be）7,000 kilometres long，and it will stop the wind from 2 ________（blow）the earth away．It 3 ________already ________（save）a lot of land．

    Wang Feng is a worker at Yulin in Shanxi Province．He 4 ________ （work）on the Great Green Wall with many other people．We 5 ________ （visit）him at his workplace and when we saw him he 6 ________ （work）among the trees．He told us something about his work“We must 7 ________ （plant）many thousands of trees every year，”he said“You see all those small trees over there on that hill? That was sand five years ago．Now it's a young forest! In a few years’ time，we 8 ________（cover）those mountains with trees，too!”He pointed to the high mountains far away．

    Was it difficult 9 ________ （work）on the Great Green Wall?

    Yes，It’s hard work．but it's very important．The only problem is we have to 10 ________（grow）our own food．But thanks to the Great Green Wall，the land produces more crops．So the more trees there are，the better harvest we have．”