___the safety of the gas,the government has checked the city's gas supply system.
A.toensureB.ensuringC.HavingensuredD.Tohaveensured答案;A。为什么不选D...
A. to ensure
B.ensuring
C.Having ensured
D.To have ensured
答案;A 。 为什么不选D 展开
B.ensuring
C.Having ensured
D.To have ensured
答案;A 。 为什么不选D 展开
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