题目内容
(请给出正确答案)
[单选题]
A. agoB. beforeC. sinceD. after
A.ago
B. before
C. since
D. after
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A.ago
B. before
C. since
D. after
A.PNP型Ge管
B.PNP型Si管
C.NPN型Ge管
D.NPN型Si管
E.以上说法都不对