1. Some viruses incubate very rapidly.
    有些病毒繁殖得很迅速.

2. Much later, scientists discovered viruses.
    过了很久以后，科学家发现了病毒。

3. Meanwhile, another powerful killer of bacteria and viruses was discovered, again by accident.
    与此同时，人类又发现了一种杀灭细菌和病毒的有效药物，这次也纯属偶然。