题目内容：

    With an improved economy，many travelers have been buying first or business class seats，leaving fewer for upgrades（升级）.Here are some strategies for getting a free upgrade.

1. Fly a lot.

This is the most common way to earn a free upgrade. Most airlines reserve some spaces for travelers who fly at least 5，000 miles per year. Five years ago，this meant half or more of domestic（国内的）first class travelers sat up front for free. But now，airlines are selling more high-price seats，so on popular routes it is not unusual for more than 20 travelers to compete for one or two upgrades. But on routes with fewer business class travelers，free upgrades remain more plentiful.

2. Use miles.

If you're not a frequent traveler but still have some miles to fly，you may be able to use them for an upgrade. Be careful，though，as many airlines now ask not just for miles but also a cash co-pay. One example: on flights to Europe，American Airlines charges 5，000 miles，plus $110，for a one-way upgrade from discounted economy class to business class. For most domestic upgrades，American Airlines wants 15，000 miles plus $ 75.

3. Get lucky.

Sometimes airlines overbook coach（经济舱），and a few travelers get no seats. Agents try to ensure the airline's most loyal travelers get the nod（被选中）. Agents usually have some flexibility to make sure the plane is full and takes off on time. So it's the easiest way for them to do it-they might upgrade someone else out of order.

4. Save a life.

Flight attendants don't usually upgrade passengers, even when empty seats remain. Doctors and nurses who answer an emergency call are sometimes an exception. If they comfort a passenger, flight attendants might allow them to sit in business or first class for the rest of the flight.

1.What might be the main topic of the passage?

A. The ways to get upgraded on a plane.

B. How to get on the flight safely and on time.

C. The best ways to get free flight tickets.

D. How to save a life on a plane quickly.

2.Who can have the chance to get a free upgrade?

A. The person who always obeys the rules on the flight.

B. The person who doesn't have to look after a patient.

C. The person who is a friend of the flight attendants.

D. The person who flies a lot and has a long flying distance.

3.Why might medical personnel be allowed to sit in business or first class sometimes?

A. Because they would like to talk with flight attendants kindly.

B. Because they want to have a better rest after a long journey.

C. Because they need to treat a passenger who is in emergent condition.

D. Because they are tired of staying with common passengers.

4.Where can we find the passage?

A. A life guide. B. A travel guide.

C. A shopping guide. D. A pilot guide.