virus:病毒????，它是一个可数名词，virus的复数形式是viruses
The drug attenuates the effects of the virus.这药能减轻病毒的危害。
The test could be used to screen healthy people to see if they are carrying the virus.这项测试可以用来检查健康人群，看他们是否携带该病毒。
There are many different strains of flu virus.有许多不同类型的流感病毒。
virus 当做“病毒”理解时，是可数名词；当做“毒素”理解时，是不可数名词
