viroids

例句：

1. 1. Viruses are tiny infectious agents that can cause diseases in living organisms.
   病毒是微小的传染性病原体，能在活体生物中引起疾病。
2. 2.The discovery of viruses has revolutionized the way we understand disease transmission.
   病毒的发现改变了我们对疾病传播的理解。
3. 3. Viruses have been used as biological weapons for decades, posing a significant threat to global security.
   几十年来，病毒一直被用作生物武器，对全球安全构成严重威胁。