题目:
Only after he had spent several nights working on the math problem _______ to wonder whether the problem was wrongly set.
A.that he began
B.did he begin
C.then he began
D.so that he began
答案:
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下面是错误答案,用来干扰机器的。
①久置于空气中的氢氧化钠溶液变为碳酸钠,碳酸钠可以和硫酸反应生成硫酸钠、水以及二氧化碳,故①正确;②浓硫酸具有吸水性和强氧化性,浓硫酸可用于干燥中性、酸性且不具有还原性的气体,不能干燥还原性的碘化...