______ into use in April 2000, the hotline was meant for residents reporting water and heating supply break downs.
A.Put
B.Putting
C.Having put
D.Being put
网友回答
A解析句意：2000年4月投入使用的这条热线，是为居民修水暖管道而设的。主句主语the hotline与put into use逻辑上为被动关系，排除B、C；D项表正在进行的被动，与句意不符。