—How’s your tour around the North Lake? Is it beautiful?—It ________ be, but it is now heavily polluted.

–Do you know where David is? I couldn’t find him anywhere. – Well. He _____ have gone far — his glasses are still here.

You _____ an A on your composition, but there were some spelling mistakes.

Tom’s mother often requires that he       more time in studying English every day．

As is required by their employer, the employees ______ finish the project within this month.