阅读材料，回答下面的题目。
The Diminishing Scientific Leadership of the U, S.With the rapid globalization of science itself ( more than 40 percent of scientific Ph.D. students trained in the United States are now foreign nationals, roughly half of whom return to their countries of origin ) , the once undisputed U.S.scientific lead, whether relevant to product lead or not, is diminishing.
The competition of foreign students for positions in U.S.graduate schools has also contributed to making scientific training relatively unattractive to U.S.students, because the rapidly increasing supply of students has diminished the relative rewards of this career path. For the best and brightest from low-income countries, a position as a research assistant in the United States is attractive, whereas the best and brightest U.S.students might now see better options in other fields. Science and engineering careers, to the extent that they are opening up to foreign competition ( whether imported or available through better communication ) , also seem to be becoming relatively less attractive to U.S. students.
With respect to the role of universities in the innovation process the speculative boom of the 1990s( which, among other things, made it possible to convert scientific findings into cash rather quickly ) was largely unexpected.The boom brought universities and their faculties into much closer contact with private markets as they tried to gain as much of the economic dividends from their discoveries as possible. For a while,the path between discoveries in basic science and new flows of hard cash was considerably shortened. But during the next few decades, this path will likely revert toward its more traditional length and reestablish in a healthy way, the more traditional ( and more independent ) relationship between the basic research done at universities and those entities that translate ideas into products and services.
In the intervening years, another new force also greatly facilitated globalization: the rapid growth of the Internet and cheap wide-bandwidth international communication. Today, complex design activities can take place in locations quite removed from manufacturing, other business functions and the consumer. Indeed, there is now ample opportunity for real-time communication between business functions that are quite independent of their specific locations. For example, software are development, with all its changes and complications, can to a considerable extent be done overseas for a U.S.customer.Foreign call centers can respond instantly to questions from thousands of miles away.The result is that low-wage workers in the Far East and in some other countries are coming into even more direct competition with a much wider spectrum of U.S. labor: unskilled in the case of call centers; more highly skilled in the case of programmers.

A . the scientific leadership of the U．S．
B . the shortage of scientists in the U．S．
C . the rapid globalization of science
D . better communication and globalization

参考答案：A

参考解析：

【答案】A
【解析】第一段开头即点明了文章主旨：“the once，undisputed U．S．scientific lead…is diminishing．”。其他三段从三个方面对此作了阐述：“scientific training relatively unattractive to U．S．students”，“during the next few decades，this path likely will revert toward its more traditional length and reestablish， in a healthy way，the more traditional relationship…”，“another new force also greatly facilitated globalization”。由此可知，本文着重讨论的是科学全球化造成美国科技领先地位的下降。主旨归纳题，应明确文章的中心思想。