来自苏琪的问题
Ifthenewsafetysystem_______touse，theaccidentwouldneverhavehappened．（）A.hadbeenputB.wereputC.shouldbeputD.wouldbeput
Ifthenewsafetysystem_______touse，theaccidentwouldneverhavehappened．（）
A.hadbeenput
B.wereput
C.shouldbeput
D.wouldbeput
