单选题 One of the prominent factors that has made CIs presence in South Korea particularly tougher because ______.

A、 a few bad apples have dented the reputation of the American servicemen in South Korea
B、 many Koreans have biased views against American servicemen
C、 some foreign countries had their soldiers present in South Korea in the past
D、 South Korea no longer needs U.S. economic aid

【正确答案】 A

【答案解析】题目问的是主要因素，应选A；B和D是辅助因素；C文中没有提及。