It is thought that one billion people I the world, __________is half the word’s workers, earn their living by farming.

A. if    B. that    C. which   D. what

 The teacher insisted that I ____ a mistake and insisted that I ____ the physics problem again.

   A. made; did     B. made; do     C. make; do        D. make; did

--Hi, Tracy, you look tired.

--I am tired. I__________ the living-room all day.

A. painted                        B. have been painting    

C. had painted                    D. have painted

—Did you know more about the mine accident?

—Oh, sorry, I had no idea. I ____the Rescue Center now.

A. will be phoning B. am to phone             C. will phone                D. phone

This is the second time I _______ the Himalayas as a college student.

1. A.
   climb
2. B.
   had climbed
3. C.
   climbed
4. D.
   have climbed