A、High school teachers. B、Taxi drivers. C、Waiters. D、Fruit sellers, D根据文章最后提到的内容，可知答案是D

When they advise your kids to "get an education if you want to raise your income", they tell you only half the truth. What they really mean is to get just enough education to provide manpower for your society, but not too much that proves an embarrassment to your society.
    Get a high school diploma, at least. Without that, you are occupationally dead, unless your name happens to be George Bernard Shaw or Thomas Alva Edison then you can successfully drop out in grade school.
    Get a college degree, if possible. With a B.A., you are on the launching pad. But now you have to start to put on the brakes. If you go for a master’ s degree, make sure it is an M.B.A., and only from a firstrate university. Beyond this, the famous law of diminishing returns begins to take effect.
    Do you know, for instance, that long-haul truck drivers earn more in a year than full professors can? Yes, the average 1977 salary for those truckers was $ 24,000, while the full professors managed to average just $ 23,930.
    A Ph. D is the highest degree you can get, but, except in a few specialized fields such as physics or chemistry, where the degree can quickly be turned to industrial or commercial purposes, you are facing a dim future. There are more Ph. Ds unemployed or underemployed in this country than in any other part of the world by far.
    If you become a doctor of philosophy in English or history or anthropology or political science or language or—worst of all—in philosophy, you run the risk of becoming overeducated for our national demands. Not for Our needs, mind you, but for our demands.
    Thousands of Ph. Ds are selling shoes, driving cabs, waiting on tables and filling out fruitless applications month after month. And then maybe taking a job in some high school or backwater college that pays much less than the janitor earns.
    You can equate the level of income with the level of education only so far. Far enough, that is, to make you useful to the gross national product, but not so far that nobody can turn much of a profit on you.