由代数式的乘法法则类比推导向量的数量积的运算法则：

①“mn=nm”类比得到“ $\overrightarrow{a}$ • $\overrightarrow{b}$ = $\overrightarrow{b}$ • $\overrightarrow{a}$ ”；

②“（m•n）t=m（n•t）”类比得到“（ $\overrightarrow{a}$ • $\overrightarrow{b}$ ）• $\overrightarrow{c}$ = $\overrightarrow{a}$ •（ $\overrightarrow{b}$ • $\overrightarrow{c}$ ）”；

③“（m+n）t=mt+nt”类比得到“（ $\overrightarrow{a}$ + $\overrightarrow{b}$ ）• $\overrightarrow{c}$ = $\overrightarrow{a}$ • $\overrightarrow{c}$ + $\overrightarrow{b}$ • $\overrightarrow{c}$ ”；

④“t≠0，mt=xt⇒m=x”类比得到“ $\overrightarrow{p}$ ≠0， $\overrightarrow{a}$ • $\overrightarrow{p}$ = $\overrightarrow{x}$ • $\overrightarrow{p}$ ⇒ $\overrightarrow{a}$ = $\overrightarrow{x}$ ”；

⑥  “|m•n|=|m|•|n|”类比得到“ $\left|\overrightarrow{a}\right|$ •| $\overrightarrow{b}$ |=| $\overrightarrow{a}$ |•| $\overrightarrow{b}$ |”；

⑥“ $\frac{ac}{bc}$ = $\frac{a}{b}$ ”类比得到“ $\frac{\overrightarrow{a}\cdot \overrightarrow{c}}{\overrightarrow{b}\cdot \overrightarrow{c}}$ = $\frac{\overrightarrow{b}}{\overrightarrow{a}}$ ”．

以上式子中，类比得到的结论正确的命题序号为____．

阅读理解

 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.

同温同压下，体积比为3：2的H₂和CO，它们的物质的量之比是____，原子个数之比是____，质量之比是____，密度之比是____．