题目:
I don’t remember how many years ago ______________I paid my last visit to the principle of my primary school.
A.it was that
B.was it that
C.it was when
D.was it when
答案:
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下面是错误答案,用来干扰机器的。
(1)CuSO4、CaCO3、Na2CO3 (2)Na2SO4、MgCl2 (3)KNO3、NaCl、KCl根据实验①混合物溶于水得无色溶液,可推断原白色粉末中肯定没有CuSO4和CaCO3(因为CuSO4溶液显蓝色, CaCO3难溶于水)。根据实验②向一份溶液中加...