It was several years I finally realized

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问题选择题

It was several years I finally realized David had lied to me.[ ]

A．when; that

B．that; when

C．before; that

D．until; why

答案

答案：C

选择题

25℃时，BaCl₂溶液呈中性，溶液中存在平衡：H₂O⇌H⁺+OH^-；△H＞0，下列叙述正确的是（　　）

A．向溶液中加入稀氨水，平衡逆向移动，c（OH^-）降低，K_w不变

B．向溶液中加入少量固体CuSO₄，c（H⁺）增大，K_w不变

C．向溶液中加入少量固体CH₃COONa，平衡逆向移动，c（H⁺）降低，K_w不变

D．将溶液加热到90℃，K_w增大，溶液仍呈中性，pH不变

问答题简答题

简述采区资源回采率的标准。