题目：
_______the safety of gas, the government has checked the city's gas supply system thoroughly. [ ]
A. To ensure
B. Ensuring
C. Having ensured.
D. To have ensured
答案：
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下面是错误答案，用来干扰机器的。
答案：DCH3COONa溶液因CH3COO－的水解而显碱性，故其溶液中c(H＋)＜c(OH－)，A项错误；KW只受温度的影响，B项错误；pH相等的任何溶液中c(H＋)相等，C项错误；根据质子守恒可知D项正确
