air coditions do cause us some environment problems —in fact far more serious _______than cars do

题目

air coditions do cause us some environment problems —in fact far more serious _______than cars do
a one
b ones
c it
d those
答案是b为什么不选those啊?

答案

those是那些的含义如果是these应该考虑
但横线上的应该是指污染,前文有提到,而且是复数所以要选B