Most environmental problems exist because adequate measures for preventing them___taken in the past.A.was not B.were not
问题描述：
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 请说明原因,
答
B.were not
Most environmental problems(主语） exist（谓语） because（引导原因状语从句） adequate measures（从句的主语） for preventing them （主语的定语）were not taken（被动语态做谓语） in the past