Most environmental problems exist because adequate measures for preventing them_____taken in the pa
A、was not
B、were not being
C、were not
D、being not
选哪个详细 分析下各个选项.这个题对我很重要 .感谢帮助.还有 been 和being 该怎么区别 ?做被动的时候应该用哪个啊?10分全部送上 .