题目内容：
根据以下内容回答题：The rise of multinational corporations (跨国公司), global marketing, new communications technologies, and shrinking cultural differences have led to an unparalleled increase in global public relations or PR.
Surprisingly, since modern PR was largely an American invention, the U.S. leader ship in public relations is being threatened by PR efforts in other countries. Ten years ago, for example, the world's top five public relations agencies were American owneD． In 1991, only one was. The British in particular are becoming more sophisticated and creative. A recent survey found that more than half of all British companies include PR as part of their corporate (公司的) planning activities, compared to about one third of U.S. companies, it may not be long before London replaces New York as the capital of PR.
Why is America lagging behind in the global PR race? First, Americans as a whole tend to be fairly provincial and take more of an interest in local affairs. Knowledge of world geography, for example, has never been strong in this country. Secondly, Americans lag behind their European and Asian counterparts (相对应的人) in knowing a second language. Less than 5 percent of Burson Marshall's U.S. employees know two languages. Ogilvy and Mather has about the same percentage Conversely, some European firms have half or more of their employees fluent in a second language. Finally, people involved in PR abroad tend to keep a closer eye on international affairs. In the financial PR area, for instance, most Americans read the Wall Street Journal. Overseas, their counterparts read the Journal as well as the Financial Times of London and The Economist, Publications not often read in this country.
Perhaps the PR industry might take a lesson from Ted Turner of CNN (Cable News Network). Turner recently announced that the work "foreign" would no longer be used on CNN news broadcasts. According to Turner, global communications have made the nations of the world so interdependent that there is no longer any such thing as foreign.
According to the passage, U.S. leadership in public relations is being threatened because______. A．an unparalleled increase in the number of public relations companies
B．shrinking cultural differences and new communications technologies
C．the decreasing number of multinational corporations in the U.S.
D．increased efforts of other countries in public relations
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