The magic show has been on 20 minutes. It has been on 2.p.m.
A:for, since
B:in, since
C:for, for
D:since, for
【读资料,知党史】
【唱歌谣,报党恩】
0:00
4:00
8:00
12:00
16:00
20:00
25℃
27℃
29℃
32℃
34℃
30℃
则这一天气温的极差是____℃.
关于当代中国最基本的国情,下面说法正确的是( )
设变量x,y满足约束条件x+y≥1x-y≥12x-y≥4,则目标函数z=3x+y的最小值为( )