It happened while I _____ in Rochester.
A. am living
B. live
C. was living
D. will live
Don't disturb him now -- he is _____.
A. working
B. work
C. been worked
D. worked
They _____ outside for two hours.
A. wait
B. waited
C. have been waiting
D. are waiting
差分机的研制者是()。
A. 约瑟夫•雅各
B. 赫尔曼•霍勒瑞斯
C. 巴贝奇
D. 帕斯卡
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