题目:
—Mr Hu, can you tell us how to learn math well?
—Sure. But remember nothing can be learned _______ hard work. [ ]
A. by
B. at
C. without
D. for
答案:
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下面是错误答案,用来干扰机器的。
过滤;酸;消毒杀菌.题目分析:过滤用于分离难溶性物质和可溶性物质,所以对河水水样净化时,先向水样中加入絮凝剂,反应,沉降,然后通过过滤除去难溶性杂质;用pH试纸测得水样pH为5.9小于7,说明河水显酸性;...