to this additional advice:

Book on Tuesday, Wednesday and Thursday. That's when airlines most often offer special sales.

Buy in advance, but not too early. The best time is four to six weeks before traveling. In general, prices for any given flight are highest eight to ten weeks and two to three weeks in advance.

　　Make use of social media. Airlines are giving more benefits to travelers who interact with them on Twitter and Facebook. But those specials are often gone within hours.

Choose the stable or the lowest? The fares of some so-called discount airlines, such as JetBlue, Air-Tran, Southwest and Frontier, are less changeable than other airlines, so you can feel more confident that the price will stay the same. But the fares aren't always the lowest.

In all, there's no way to guarantee the best fare, but researching different airlines' fares can be the only way to get a good deal.

4. What can we infer from the first sentence of the text?

　　A. Airlines often play games with passengers.

B. Passengers are unable to search for airfares.

C. It's difficult for passengers to get the best price.

D. Airfares are set in different situations.

5. By using a lot of figures, the author intends to ________.

A. discover the rules behind airfares B. prove airfares can vary widely

C. guarantee passengers a low price

D. show there is standard price for every single airline

6. If you want to take a flight on Christmas, which time can be the best to book a ticket?

　　A. September 15th B. October 15th C. November 15th D. December 15th

7. Passengers are advised to book flights _________.

A. at the lowest price by comparing as many airlines

B. with airlines which are famous for offering discount prices

C. through two apps on smart phones D. on some special websites