根据短文内容，用方框中所给单词的正确形式填空，每空限用一次，有一项多余。

    Most people have their jobs. Some people are . Either they have very interesting jobs or they make a lot of money. Most people don't have such good luck. Either their jobs are not very interesting or they don't make money. The most interesting jobs are often the most difficult. People spend a long time how to do them. Doctors study for at least six years after school.

    Some jobs need young people. Football stars are usually under 35 because older people cannot play it very . However, old people can also do many jobs. Writers, artists and scientists usually work until they die.