environmental problems exist because adequate measures for preventing them
问题描述：
environmental problems exist because adequate measures for preventing them
Most environmental problems exist because adequate measures for preventing them_ taken in the past.
A.was not
B.were not
C.were not being
D.being not
想问问其他为什么不选呢?
答
这句话的意思是：大多数环境污染问题的存在是因为充分预防措施在过去没有被重视.
首先这个句子的重点是~预防措施没【被】重视,所以答案一定要体现【被动】
句意是说污染问题还在是因为 【过去】防护措施 没被重视,而不是【过去某个时刻】没被重视,所以排除C,D
注意：（were being+过去分词 表示过去进行时的被动语态.如The builidings were being built this time last year.这些大楼去年的这个时候正在修建.）
（being not done不成结构,必须是 be being not done)
又因为是them 复数 所以选B