___the safety of the gas,the government has checked the city's gas supply system.
A.toensureB.ensuringC.HavingensuredD.Tohaveensured选哪个?...
A. to ensure
B.ensuring
C.Having ensured
D.To have ensured
选哪个? 展开
B.ensuring
C.Having ensured
D.To have ensured
选哪个? 展开
1个回答
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