题目

单项填空 在A、B、C、D四个选项中， 选出可以填入空白处的最佳选项。Mary advised that I should buy ______ iPad for my son as a birthday present. Young people are dreaming about owning______.A. a; it B. a; one C. an; one D. an; it 答案：C设a＞0，b＞0．若3是3a与3b的等比中项，则1a+1b的最小值为（　　）A．4B．2C．1D．14