A、It costs less. B、It is flexible. C、It saves time. D、It grows fast. C选项主语均为It以及选项中的costs less，flexible，saves time和grows fast表明，

Brian arrived at the San Francisco airport two hours before the flight to Paris. He was wearing three shirts, a jacket, two pairs of socks, a pair of shorts, and two pairs of jeans. He was carrying one small backpack, which was very full, but he didn’t have any other luggage. Brian needed to meet a man named Tony before he checked in for his flight. He found Tony near the Air France counter. Tony gave him a round-trip ticket and a small package.
    "Give this package to Jean-Paul at the airport in Paris. He will have a sign with your name on it. I think you can find him easily," Tony said. "You don’t have any luggage, right?"
    "Only this backpack," Brian answered. "You said I could bring one carry-on bag."
    "That’s right. One carry-on bag is fine. Have a good trip."
    "Thanks."
    Is Brian a criminal? Not at all. He is an air courier. And he paid only $110 for the round-trip ticket to Paris. Air couriers get cheap airline tickets because they take important packages and papers to foreign countries. Businesses sometimes need to get packages and papers to people in foreign countries by the next day. Often, the only way they can do this is to use an air-courier company. It is not cheap for a business to send a package with an air courier, but it is quick.
    Every year about 80,000 people worldwide travel as air couriers. The number of tickets for courier travel is growing by about 10 percent a year. However, air-courier travel isn’t for everyone. But if you have very little money, can be flexible about your travel plans, and don’t mind wearing the same clothes for a week, it can be a great way to take a vacation!
Questions 22 to 25 are based on the passage you have just heard.
22. Why was Brian wearing so many clothes for his travel?
23. What do we learn about an air courier’s job from the passage?
24. Why do businesses choose the air-courier service according to the passage?
25. What is one of the disadvantages of traveling as an air courier?