问题
选择题
. If only I ________ how to operate an electronic computer as you do.
A．had known
B．would know
C．should know
D．knew
答案
答案：D
因为if only (要是…就要了) 其后的句子要用过去式表示虚拟语气，由as you do可知，是与现在事实相反，所以选knew。
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2Z(g)+2W(g)在2L密闭容器中进行，5min后Y减少了0.5mol，则此反应的速率v为( )