— I didn't see you yesterday.
— ______ I was ill yesterday, ______ I didn't go to work.
A：Because; so
B：For; and
C：/; but
D：/; so
在“草→昆虫→青蛙→蛇”这条食物链中，你认为蛇（ ）
城市化的意义有（）
