A. have been known to scientists for years B. have only recently been discovered C. are known by everyone D. will probably remain a mystery 参考答案:B 答案解析:本篇第一段说这个问题多年来使科学家迷惑不解,但随后又说:Now they are beginning to fill in the blanks,这里“逐渐开始填补这些空白”意为“逐渐开始对此有所了解
第17题: [单项选择]男性,61岁,活动后心悸、气促5年,加重伴双下肢水肿3个月。查体:血压140/90mmHg,双肺底少许湿性啰音。心界扩大,心率130次/分,心律绝对不齐,心音强弱不等,可闻及舒张期奔马律。心尖区可闻及2/6级收缩期柔和吹风样杂音。肝肋下3cm,脾未触及,双下肢中度水肿主要鉴别要点是() A. 有无心绞痛与心肌梗死病史 B. 有无心肌炎病史 C. 有无高血压病史 D. 有无结核病史 E. 有无风湿病史 参考答案:A