题目

Imagine that the genome (基因组) is a book. The book consists of 23 chapters, with thousands of stories made up of paragraphs, words and letters on different levels. There are one billion words in the book, which makes it longer than 500 dictionaries. If I read the genome out to you at the rate of one word per second for eight hours a day, it would take me a century. If I wrote out the human genome, one letter per millimeter, my text would be as long as the River Danube. This enormous document, however, all fits inside the extremely small nucleus (核) of a tiny cell that fits easily upon t选词填空。 珍贵 宝贵 稀少 稀有 消灭 灭绝 1．银杏树是几亿年前的树种，十分( )。 2．由于以前缺乏保护，目前，中华鲟已成为( )鱼种了。 3．几只壁虎很快就把蚊子( )干净了。