任何时候基因组中都只有一小部分基因在活动。
A. 对
B. 错
Earthquakes ________ in Japan frequently because it lies in the earthquake zone.
A. was breaking out
B. was broken out
C. broke out
D. break out
Both his parents look sad. Maybe they_______ what's happened to him.
A. knew
B. have known
C. know
D. will know
Hardly _________ our walk when it began to rain.
A. we began
B. we had begun
C. had we begun
D. has we begun
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