题目内容：

    Duolingo

Over 70 million people have registered with Duolingo, a free and incredibly well-designed language learning app. Though not a replacement for proper language tuition, the app is a fun way to get the basics, or to keep yourself fresh on grammar and vocabulary, before a trip abroad. Just like a computer game, the app guides you through levels that you need to complete before advancing, and you gain experience points along the way.

* Free, iOS and Android, duolingo.com

XE Currency（货币）

XE is the go-to site for currency conversions on the web, so it’s no surprise that its app is so popular: with over 20 million downloads since launch. It has lots of business-oriented features, such as rates for previous metals and historic charts, but for the traveler it is most useful for the simple fact that it’s able to convert every world currency. It also functions offline by saving the latest updated rates.

* Free, iOS and Android, xe.com

App in the Air

App in the Air is a smart, straightforward, flight tracking app that has the best coverage of airlines and airports. It will keep you updated about flight status even if you don’t have internet coverage and help you manage your time at the airport, breaking down each flight into four stages: check in, boarding, takeoff and landing time.

* Free, iOS and Android, appintheair.mobi

Wolfram Sun Exposure

There are a few apps out there that help you manage your time in the sun safely, but this one offers the most detailed information to keep you informed. You enter your skin type and it calculates how long you can spend sunning yourself before getting burned, based on the time of day, where you are and the strength of sun cream you’re wearing. It also provides UV forecasts for your location.

* £0.79, iOS

1.If you want to know the information about the change rate of money, you can turn to      for help.

A.Wolfram. B.App in the Air.

C.XE Currency. D.Duolingo.

2.About these apps, which of the following is TRUE?

A.All of these four can be used in the same system.

B.Duolingo is an unbelievable gaming app where you gain experience points along the way.

C.You can learn the latest news about the flights with limited connectivity in App in the Air.

D.Your time in the sun safely is influenced by the brand of sun cream you’re applying.

3.The passage is intended for      .

A.teenagers. B.travelers.

C.businessmen. D.guides.