单选题
Three weeks after the suicidal bombing, the police were still hunting for bombers for they believe more were ______.
【正确答案】
B
【答案解析】on the sly偷偷地，暗地里；on the verge后跟of结构表示“在……的边缘”；on the spot当场，在现场；on the loose散漫，放荡。句意：自杀性爆炸三个星期之后，警方还在搜寻爆炸者，因为他们相信还有更多的爆炸者在暗地里行动。