He had no choice but to go on because it is their agreement that no one ______ quit the plan half way.

You ______ do it if you really don’t want to.

 —Can your friend sing?--______.

— If you listen to me, you ______ take a good rest at once.— OK, I ______ do so.

—Is John coming by train.—He should，but he ________ not.He likes driving his car.