单项选择题
A．pay their membership fees regularly B．fly overseas at least once every year C．take a domestic flight with Air France once a month D．pay for their flight at least once within twenty months
A．It is money-saving and easy to learn. B． It is a simple way to save energy. C．It is convenient and challenging D．It is done more efficiently.
A．get free tickets B．visit local scenic spots C．shop in the supermarkets D． go through the VIP passage