一袋大米重20千克,第一周吃了6千克,第三周吃了7千克.还剩下这袋大米的几分之几?
(20-6-7)÷20,
=7÷20,
=720.
答:还剩下这袋大米的720.
Wang Gang doesn't want to _____ his parents _____, so he always works hard. [ ]
A. let; down
B. turn; down
C. keep; down
D. put; down
影响有机溶剂沉淀的因素有()、()、()、()和()。