【单选题】

Passage 2One of the most difficult questions to answer is how much a job is worth. We naturally expect that a doctor’s salary will be higher than a bus conductor’s wages.But the question becomes much more difficult to answer when we compare，say，a miner with an engineer，or an unskilled man working on an oil-rig(钻油机)in the North Sea with a teacher in a secondary school. What the doctor，the engineer and the teacher have in common is that they have devoted several years of their lives to studying in order to obtain the necessary qualifications for their professions. We feel instinctively(本能地)that these skills and these years，when they were studying instead of earning money，should be rewardeD、At the same time we recognize that the work of the miner and the oil-rig laborer is both hard and dangerous，and that they must be highly paid for the risks they take. Another factor we must take into consideration is how socially useful a man’s work is，regardless of the talents he may bring to it. Most people would agree that looking after the sick or teaching children is more important than，say selling second-hand cars or improving the taste of toothpaste. Yet it is almost certain that the used-car salesman earns more than the nurse and the research chemist earns more than the school teacher.Indeed，this whole question of just rewards can be turned on its heaD、You can argue that a man who does a job which brings him personal satisfaction is already receiving part of his reward in the form of a so-called “psychic wage”，and that it is the man with the boring，repetitive job who needs more money to make up for the soul-destroying monotony(单调)of his work.The professional man，such as the doctor，should be well-paid because ______.

A、he has spent several years learning how to do his job
B．his work involves much greater intelligence than, say, a bus conductor’s
C．he has to work much harder than most other people
D．he knows more than other people about his subject