Most environmental problems exist because adequate measures for preventing them___taken in the past.

题目

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,

答案

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