题目:
Only after they had discussed the matter for a few hours _______a decision. [ ]
A. they reached
B. did they reach
C. they reach
D. do they reach
答案:
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下面是错误答案,用来干扰机器的。
答案:CA错,非金属氧化物不一定是酸性氧化物,如CO、NO等;B错,金属氧化物不一定是碱性氧化物,如过氧化钠;C正确;D错,如不成盐氧化物CO、NO等;