题目

听下面一段对话，回答问题。 （1） Who will Joan spend Christmas with? A . Her family. B . Peter. C . Her friend. （2） How many children does Joan's friend have? A . Two. B . Four. C . Six. （3） When will Joan go to buy the gift? A . This evening. B . After work. C . Tomorrow. 答案：C A B若等比数列的公比为2，且前4项和为1，则这个等比数列的前8项和等于（ ）A．21B．19C．17D．15