B. Chinese is more useful than math.

      C. Chinese is not so useful as math.

      D. Chinese and math are not useful enough.

(   ) 2. A. David and Bob don't finish his homework.

       B. David and Bob have finished his homework.

       C. David and Bob can finish their homework.

       D. David has to finish their homework, so does Bob.

(   ) 3. A. The train will leave the train station in half an hour.

       B. The train will get to the station in thirty minutes.

       C. The train has been at the train station for half an hour.

       D. The train got to the station half an hour ago.