Natural selection tends to eliminate genes that cause inherited diseases , acting most strongly against the most severe diseases ; consequently , hereditary diseases that are ___ would be expected to be very ___ , but , surprisingly , they are not .

A lethal

D perplexing

B unusual

E rare

C widespread

F acute

选AE

翻译：自然选择倾向于淘汰那些导致遗传病的基因，尤其是多数严重的疾病，由此可推，致命的的遗传病本该很少见，但令人惊讶的是，实际情况并非如此。

perplex 使复杂化，使困惑

acute 尖锐的，敏感的，剧烈的，急性的，锐角的