抗凝剂枸橼酸三钠水溶液与血液按1:9或1:4体积比例使用，条件是血细胞比容须在

A．20%～30%
B．30%～40%
C．30%～50%
D．40%～50%
E．50%～60%

Questions 1-4

What’s the speaker’s definition of jet lag？（）

A．A flight over time zones.

B．A loss of one’s characters.

C．A symptom of leg problems.

D．A condition of sleep disorders.