Which of the following is TRUE, according to the passage?

Câu hỏi: Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.
One 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 wage. 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 in the North Sea with a teacher in a secondary school. What the doctor, the engineer and teacher have is many years of training in order to obtain the necessary qualifications for their professions. We feel instinctively 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 secondhand cars or improving the taste of toothpaste by adding a red stripe to it. Yet it is almost certain that the used car salesman earns more than the nurse, and that 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 of his work. It is significant that that those jobs which are traditionally regarded as "vocations" - nursing, teaching and the Church, for example - continue to be poorly paid, while others, such as those in the world of sport or entertainment, carry financial rewards out of all proportion to their social worth.
Although the amount of money that people earn is in reality largely determined by market forces, this should not prevent us from seeking some way to decide what is the right pay for the job. A starting point for such an investigation would be to try to decide the ratio which ought to exist between the highest and the lowest paid. The picture is made more complicate by two factors: firstly by the "social wage", i.e, the welfare benefits which every citizen receives; and secondly, by the taxation system, which is often used as an instrument of social justice by taxing high incomes at a very high rate indeed. Allowing for these two things, most countries now regard a ratio of 7:1 as socially acceptable. If it is less, the highly-qualified people carrying heavy responsibilities become disillusioned, and might even end up by emigration (the so-called "brain-drain" is an evidence that this can happen). If it is more, the gap between rich and poor will be so great that it will lead social tensions and ultimately to violence.
(Adapted from: Business Insider)
Which of the following is TRUE, according to the passage?
A. It's not difficult to define the social value of a job.
B. The market used to decide what the right pay is for a job.
C. People should find a proper ratio between high and low pay.
D. Those receiving high salary should carry all responsibilities.