A big step _____ to strengthen China's health care systems since _英语解答

A big step _____ to strengthen China's health care systems since we launched an effort in 2008.
A.has been taken
B.is being taken
C.was taken
D.had been taken

人气：461 ℃　时间：2020-04-04 01:43:57

解答

A
SINCE和完成时连用~A BIG STEP显然在2008年的巨大努力之后（AN EFFORT) 所以不用过去完成时~