The old man __________ in Tibet for two years as a volunteer teacher；it is an experience he often mentions.
A．served B．serves C．is serving D．has served
Qian Xuesen tried many times _________ he found the solution to the puzzle about space technology.
A．after B．before C．since D．when
Those the exam cheat must another exam tomorrow afternoon.
A．related to; get into B．absorbed in; get through
C．connected with; get over D．involved in; get through
He admitted a lie in order to avoid .
A．having told ;punishing B．telling ;punished
C．to have told ;being punished D．having told ;being punished
I your success although you are in difficulty now.
A．am sure of B．make sure C．am sure that D．make sure that
He feels happy that he can earn he did ten years ago.
A twice that B. twice what C. twice than what D. twice than that
