—Why are you standing here, Mrs. White?—I'm waiting for my son. He _________ back from school.
A:hasn't come
B:won't come
C:doesn't come
已知A=x﹣2y,B=﹣x﹣4y+1 (1)求3(A+B)﹣2(2A﹣B)的值;(结果用x、y表示) (2)当x+12与(y﹣1)2互为相反数时,求(1)中代数式的值.
保存药品不能放在________的地方( )