2. Viruses change, or
mutate, so flu vaccines must be reformulated each year to target the most common threats.
病毒会改变或者变异,因此流感疫苗必须针对最大的威胁每年制定配方。
3. Hillis let thousands of his sorters proliferate in his computer,
mutate at random, and occasionally sexually swap genes.
希利斯让数千个排序程序在计算机中增殖,随机变异,偶尔进行有性基因互换。