单选题 16.  Over two-thirds of Americans now book their flights online. But when is the best time to book to get a cheap flight? Flying on Wednesday is a good way to save money: you'll find emptier and cheaper seats. If you can't avoid flying on a weekend, at least BOOK your flight on Wednesday; airlines tend to raise their fares on Friday and bring them back down on Monday. Another suggestion is to book your flight after the 7th of every month.