单项选择题
A．you to keep B．that you would keep C．your keeping D．that you are keeping
A．if he didn't get a flat tire B．if the flat tire hadn't happened C．had he not had a flat tire D．had the tire not flattened itself
A．the members studies the problem more carefully B．the problem would be more carefully studied C．the members had studied the problem with more care D．the problem be studied with more care