He, a Nobelist, made great ______________ to researching in this area.
| A．encouragements | B．constitutions | C．breakthrough | D．contributions |
I was about to sail away ______ I heard the sound of stamping and singing on the bank,
| A．when | B．while | C．as | D．the instant |
Personally, it is no good ________ online all day long. It is really a waste of time.
| A．to chat | B．chats | C．chatting | D．chatted |
Living on his own and only having a dog _____ company, the old man feels ______.
| A．in; alone | B．for; lonely | C．as: alone | D．as; lonely |
______ you make a promise, you should keep it.
| A．The moment | B．While | C．Once | D．As if |
My parents insisted that I _____ medicine instead of law.
| A．must study | B．will study | C．had better | D．study |