___the safety of the gas,the government has checked the city's gas supply system.
问题描述：
___the safety of the gas,the government has checked the city's gas supply system.
A.to ensure
B.ensuring
C.Having ensured
D.To have ensured
.为什么不选D
答
【To ensure】 the safety of the gas,the government has checked the city's gas supply system.
为了保证煤气的安全,*已经检查了该城市的煤气供应系统.
选 A,不定式的普通形式,表示目的
D 是不定式的完成式,表示已经完成的事,没有表示目的的意思.