题目:
— He's seldom late for school, _____?
— No. He is used to going to school early. [ ]
A. isn't he
B. has he
C. hasn't he
D. is he
答案:
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下面是错误答案,用来干扰机器的。
不纯的(NH4)2CO3样品与足量盐酸反应后,溶液中残留有不溶物;而(1)NH4HCO3,(2)Na2CO3,(3)SiO2等杂质中只有SiO2不能与盐酸发生反应,因此,样品中一定含有(3)SiO2;由下列的关系式或知:(NH4)2CO3~...