We should urge people _______ riding in cars.
A:stop
B:stopping
C:to stop
D:stopped
设变量x,y满足约束条件x≥0x-y≥02x-y-2≤0则z=3x﹣2y的最大值为( )
① xx−2−1x2−4=1
② xx−1−1=3x+1 .
—That's great! _______ foreign college students are interested in Chinese learning.