题目内容
15、Even if there is no scientific proof yet ______ secondhand smoke causes cancer, there is no reason why nonsmokers should be forced to take this risk．
A．which B．that C．when D．where
试题答案
15、B
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26．Even if there is no scientific proof yet ______ secondhand smoke causes cancer, there is no reason why nonsmokers should be forced to take this risk．
A．which B．that C．when D．Where
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