【单选题】

In the second half of the twentieth century, many countries of the South (发展中国家) began to send students to the industrialized countries for further education. They urgently needed supplies of highly trained personnel to implement a concept of development based on modernization.

But many of these students decided to stay on in the developed countries when they had finished their training.At the same time, many professionals who did return home but no longer felt at ease there also decided to go back to the countries where they had studieD、
In the 1960s, some LatinAmerican countries tried to solve this problem by setting up special "return" programs to encourage their professionals to come back home. These programs received support from international bodies such as the International Organization for Migration, which in 1974 enabled over 1,600 qualified scientists and technicians to return to LatinAmericA、
In the 1980s and 1990s, "temporary return" programs were set up in order to make the best use of trained personnel occupying strategic positions in the developed countries. This gave rise to the United NationsDevelopment Program’s Transfer of Knowledge through Expatriate (移居国外的) Nationals, which encourages technicians and scientists to work in their own countries for short periods.But the brain drain (人才流失) from these countries may well increase in response to the new laws of the international market in knowledge.
Recent studies forecast that the most developed countries are going to need more and more highly qualified professionals around twice as many as their educational systems will be able to produce, or so it is thought.As a result there is an urgent need for developing countries which send students abroad to give preference to fields where they need competent people to give muscle to their own institutions, instead of encouraging the training of people who may not come back because there are no professional outlets for them.And the countries of the South must not be content with institutional structures that simply take back professionals sent abroad, they must introduce flexible administrative procedures to encourage them to return. If they do not do this, the brain drain is bound to continue.
According to the passage, the problem of the developing countries will continue ______.
A、as long as the developed countries need more qualified professionals than they can educate domestically
B、as long as the developing countries are content with their present institutional structures
C、unless those countries stop sending large number of students to be trained abroad
D、if their governments fail to make administrative adjustments concerning the return procedures of their professionals