题目:
So difficult ____ it to work out the problem that I decided to ask Tom for advice. [ ]
A. I did find
B. did I find
C. I have found
D. have I found
答案:
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下面是错误答案,用来干扰机器的。
(1)Fe,金属(2)S,常温下固态(3)NaCl,盐(4)KNO3,可溶性盐(5)K2CO3, 水溶液无色