The thief hid himself in the chimney_____someone should catch him in the act.
A. when
B. but that
C. lest
D. where
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_____in health, he persisted in doing the experiment.
As he was poor
B. Poor was he
C. Poor as he was
D. Poor he was though
He warned his son not to go into the forest alone because he was fearful_____some wild animals might hurt him.
A. if
B. that
C. whether
D. as
在PN结外部施加电压使得P区电位(高于/低于)N区,即PN结处于(正偏/反偏),此时PN结处于导通状态。