教育理念

确保授权用户或者实体对于信息及资源的正常使用不会被异常拒绝，允许其可靠而且及时地访问信息及资源的特性是（）。

A、完整性

B、可用性

C、可靠性

D、保密性

Searching for airfares often seems like a game that passengers are bound to lose.

Prices change from day to day, even minute to minute. Looking through multiple websites for the best deal can be a big challenge. Even when you do book, there’s no guarantee that you are going to get the best price.

“You just don’t know when to pull the trigger. It’s not like buying anything else I can think of,” said George Hobica, founder of Airfarewatchdog.com.

Harriet Levy paid $179 for a recent round-trip flight on American Airlines between New York and Fort Lauderdale, Florida. Sitting just one row behind her, Shirley Harrison paid $215. A few rows back, Ellis and Dianne Traub paid $317 each. There were at least 12 fares on the flight, ranging from $169 to $360.

There’s no reason for it, Harrison said.

Fares can vary significantly in just a few hours. One Delta flight from New York to Los Angeles jumped from $755 to $1,143 from a Friday to Saturday in late April, then fell to $718 on Sunday.

The flight was one of a dozen the Associated Press (美国联合通讯社)followed over three months for a vacation between July 16 and 22. The number one finding: avoid booking tickets on weekends. It’s the most expensive time to buy.

There’s no way to guarantee the best fare. But before booking, travelers should pay attention to this additional advice:

● Book on Tuesday, Wednesday and Thursday. That’s when airlines most often offer 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 like exclusive (独家) sales to travelers who interact (互动) with them on Twitter and Facebook. Those specials are often gone within hours.

● The so-called discount airlines – JetBlue, Air-Tran, Southwest and Frontier – adjust their fares less frequently than other airlines, so you can feel more confident that the price will stay the same. But their prices aren’t always the lowest. Researching multiple airlines’ fares is the only way to get a good deal.

小题1: What can we infer from the first sentence of the text?

A．Passengers are unable to search for airfares.

B．Airlines often play games with passengers.

C．Airfares are set in different situations.

D．It’s difficult for passengers to get the best price.小题2:The underlined phrase “pull the trigger” in Paragraph 3 probably means _______.   

A．startsearching

B．getthehighestprice

C．makeapurchase

D．getonboardtheplane小题3:By using a lot of figures, the author intends to _______.

A．show there is standard price for every single airline

B．discover the rules behind airfares

C．guarantee passengers a low price

D．prove airfares can vary widely小题4:Passengers are advised to book flights _______.

A．in the middle of the week

B．on special websites

C．several months before traveling

D．with airlines which are famous for offering discount prices

上消化道出血病因诊断的首选检查措施为

A．便常规检查
B．胃镜检查
C．选择性动脉造影
D．X线钡餐检查
E．吞线试验

当同时存在水、电解质和酸碱平衡失衡时，首先应

A．调节容量不足
B．调节Cl^-不足
C．调节酸碱失衡
D．调节K⁺不足