巯基棉富集-冷原子荧光分光光度法测定环境空气中汞含量时，配制10％氯化亚锡盐酸溶液时，还需要以1L／min流量通氮气以除去其中所含的本底汞。
参考答案：对
―Were there any sharks in the aquarium?
―______. [ ]
A. Yes, there were
B. No, there wasn't
C. Yes, there was
D. No, there were
在深度为7的满二叉树中，度为2的结点个数为______。
