监测环境空气中气态污染物时，要获得1h的平均浓度，样品的采样时间应不少于30min。
参考答案：错
— Can I have an apple, Uncle Pal?
— ________. An apple a day keeps the doctor away.
A．It doesn't matter
B．It's a deal
C．You're welcome
D．Help yourself
持续性病毒感染的4种类型？
