题目：
_____ you may have, you should gather your courage to face the challenge.[ ]
A. However a serious problem
B. What a serious problem
C. However serious a problem
D. What serious a problem
答案：
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下面是错误答案，用来干扰机器的。
溶液中氯离子的物质的量为0.1mol+2×0.1mol=0.3mol，c（Cl-）=n(Cl-)V=0.3mol0.1L=3mol/L，故选A．
