Helen _____ go on the trip with us, but she isn't quite sure yet. [ ]

A. shall

B. must

C. may

D. can

关于输血速度的描述，下列哪个是错误的

A．小儿每分钟约10滴
B．一次输血的总时长不宜超过4小时
C．对失血性休克，应快速输入所需血量
D．心脏病人宜每分钟1ml
E．成人一般调节在每分钟4～6ml