We can see light in his office. He___________ be in his office.

－ Do you think the English class is _____________?－ Yes, I enjoy it very much. 

--- I heard they went skating in the mountains last winter. --- It ______ true because there was little snow there.

Please do not feed the fish; they _____ die if they eat too much.

—Look! Is that Mr. Green?—It          be Mr. Green. He has gone to Shanghai.