题干
_________to nuclear radiation, even for a short time, may produce variants of genes in human bodies.
A：Being close
B：Having been closed
C：Closed
D：After being closed
答案(点此获取答案解析）
A
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的两处，它们间库仑力的大小为
。两小球相互接触后将其固定距离变为
，则两球间库仑力的大小为www.ks5u.com