He ________ to get her on the phone, but he didn’t get through it.
A. was trying
B. had been trying
C. tries
D. has tried
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He ________ the door and after that he had a drink at a small cafe.
A. had been painting
B. has painted
C. has been painting
D. was painting
He said that he ________ the novel and had not finished it yet.
A. had been writing
B. has written
C. writes
D. is writing
The man ________ there in the sun for a long time and got his face burnt.
A. has stood
B. was standing
C. had been standing
D. is standing
在血清诊断试验中不同实验室或不同的仪器对同一未知样本做检测，目的是评价（ ）
A. 试验可靠性
B. 试验实用性
C. 试验真实性
D. 试验敏感性
E. 试验特异性
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