为了参加2011年西安世界园艺博览会，某公司用几辆载重为8吨的汽车运送一批参展货物．若每辆汽车只装4吨，则剩下20吨货物；若每辆汽车装满8吨，则最后一辆汽车不空也不满．请问：共有多少辆汽车运货？

下列关于变异的叙述中，正确的是（　　）

• 阅读下面短文, 根据文中意思, 从方框中选出恰当的词。

 These days, more and more students in the UK are taking a “gap year” between their graduation from school and their university studies. This means that they take a year off to do something else, before the ____ their studies.

   For most students, spending time in____ countries is the favorite activity – and Australia is the favourite place to go.

   Many parents, teachers and business people____  that traveling can teach important values.

   “After a year of traveling, I felt I’d grown up. I had____  the importance of relationships with people, on all sorts of levels.”

   There are many companies around the world that welcome these ____ on their projects – helping people in poorer countries., or____  in your home country. Although you don’t get paid for your work, this kind of work can teach important____ decision- making and finding answers to problems, for example – that will help a student in a ____ one day.

Finally, getting some knowledge and experience in an area you hope to study or work in one day will always be very____ .

If several university graduates are asking for the same job , gap year work experience allows you to say, “ I’ve already had some ____ of this kind of work.”And that can get you the job!