单选题 If a fever continues to exist, a doctor should be called since this may mean that a more serious infection is present.
【正确答案】 B
【答案解析】to continue to exist“持续，坚持”。其余选项或多或少与“消失”有关。句子大意：如果高烧不退，就应该请医生来，因为这可能意味着有更严重的感染。