She's my ____. [ ]
A. brother
B. sister
C. father
答案：B
8．－This is a gas station! And you_________know smoking is forbidden here.
－Oh, terribly sorry.
A．will
B．can
C．may
D．Must
二重积分化为累次积分后，累次积分的积分上限必须大于积分下限。
