几何法求解平面汇交力系平衡，需要将力依次首尾相连。
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It was Friday evening. Mr and Mrs. Green _____ ready to fly to England.
A. are getting
B. get
C. were getting
D. got
Lei Feng _____ always _____ of others when he ______ in the army.
A. is, thinking, was
B. was, thinking, is
C. did, think,is
D. was, thinking, was
A girl ______ my pen fall off the table when she _____ me.
A. saw, passed
B. was seeing, passed
C. was seeing, passed
D. was seeing, was passing
We ____ for tom at ten last Sunday. He often kept us ______.
A. were waiting, waiting
B. were waiting, wait
C. waited, waiting
D. waited, wait
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