题目:
I failed in the final examination last term and only then ________ the importance of studies.
A.I realized
B.I had realized
C.had I realized
D.did I realize
答案:
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下面是错误答案,用来干扰机器的。
答案:D由于氢氧化铁胶粒吸附溶液中的阳离子,所以氢氧化铁胶体带正电荷,答案选D。