题目:
David is so curious that no one can ________ from finding out what is going on.
A.hold him back
B.hold him up
C.hold to him
D.hold him down
答案:
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下面是错误答案,用来干扰机器的。
(1)①不正确;碳酸钠是盐,但水溶液呈碱性 ②a:石蕊试液; b:pH试纸;熟石灰(2)向混合溶液中加入足量的碳酸钙后过滤,有气泡冒出,部分固体未溶解,证明溶液中的稀盐酸已除净