问题补充:
People cut down too many trees, the greenhouse effect becomes more and more serious.
A. so
B. because
C. although
D. if
答案:
(答案→)A. so
B. because
C. although
D. if
解析:so 因此;because 因为;although虽然,尽管; if是否,如果。句意:人们砍伐了太多的树木,因此温室效应变得越来越严重。结合语境可知选A。