题干

通过对我们吸入空气和呼出气体成分的研究,比较人体吸入的空气和呼出的气体中所含有二氧化碳、氧气、水蒸气的多少,得到初步结论,并完成下表:

实验步骤 实验现象 实验结论
 (1)用排水法收集两瓶呼出气体\\
(2)向一瓶空气中和一瓶呼出的气体中分别加入少量澄清的石灰水________
 (3)将燃着的木条分别插入盛有空气和呼出气体的集气瓶中________
(4)取两块干燥的玻璃片,对着其中的一块呼气,观察玻璃片上水蒸气的情况,并与另一块放在空气中的玻璃片作对比________
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 Secrets of Web Travel Sites

Booking a trip on an online travel siteis convenient, but comes with its own set of problems.

1 They who's on a Mac and who's on a PCand who's going to spend more.

Last year, US travel research companyOrbitz tracked people's online activities to test out whether Mac users spendmore on travel than PC users. On average, Mac users lay out US$20-30 more pernight on hotels and go for more stars. according to the Wall Street Journal. Asa result, online• travel sites show these users more expensive travel optionsfirst. To avoid inadvertently paying more, sort results by price.

 Their software doesn't always hook up to thehotel's system.

A guaranteed reservation is almostimpossible to come by anywhere — but the risk of your flight or hotel beingoverbooked increases with third-party providers. The middle-man's softwareisn't immune to system errors, so always call the hotel or airline to make sureyour booking was processed.

 Don't be fooled by packages: Often, they'relow-end items grouped together.

Ever notice how travel sites recommend ahotel, a rental car, and tour package all in one click? These deals usuallyfeature travel that no one wants, like flights with multiple layovers.

Check the fine print.

 You could miss out on loyalty points.

Third-party providers can get betweenyou and frequent flyer miles or points. Many hotel loyalty programmes don'trecognise external sites, others award only minimum points and exclude specialoffers, like double points on hotel stays.

 Once your trip is purchased, you're on yourown.

An online travel agency can't provideassistance the same way an agent can if a flight is cancelled or a room issubstandard. Basically, when you arrive at the airport or hotel, you're justanother client who booked at the lowest rate.