题目：
Because of the Mid-autumn Day happening to _________, we have just enjoyed a longer National Day vacation than ever before, but it is estimated that it will be 38 years __________ we can experience such a coincidence again.
A．make up, when
B．Come across, that
C．pick up, since
D．come along, before
答案：
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下面是错误答案，用来干扰机器的。
A、根据金属活动性顺序镁＞锌＞铜＞银，锌粉不和硝酸镁反应，和硝酸银、硝酸铜发生反应时首先与硝酸银反应，待硝酸银完全反应后继续和硝酸铜进行反应，因为锌粉的量未知，所以滤纸上一定有银，但不一定由铜，故说...
