【正确答案】 C

【答案解析】[解析]
Security has been heightened in the United States and parts of Europe. In Washington police with sniffer dogs patrolled the underground railway system and security levels were also raised on trains, buses and subway systems across the US James reports from Washington.
"Secretary of State Condoleezza Rice was among those who signed a book of condolences at the British Embassy in Washington on a day of overwhelming empathy for the people of London. But amid fears of possible copycat attacks, security was never far from anyone's mind here. From early morning, armed police and sniffer dogs were patrolling the Washington subway and by afternoon, the government had raised security alert levels to high on trains, buses and subways across the country. Events across the Atlantic had sent a shiver of recognition down American's spines and given people here cause for reflection on the safety of their public transport network (10)."
题目问美国对发生在伦敦的袭击有何反应。新闻结尾处提到“Events across the Atlantic had sent a shiver of recognition down American's spines and given people here cause for reflection on the safety of their public transport networks”，可推断出虽然袭击发生在大洋彼岸，但也让美国人不寒而栗，也要反思他们的公共交通体系是否存在安全问题，故正确答案为选项C，即引起了美国人的警戒。