propagation path

例句：

1. 1.The propagation path of the disease is unknown.
   这种疾病的传播路径未知。
2. 2. The researcher found a new transmission path for the virus.
   研究人员发现了病毒的新传播途径。
3. 3. The scientists are studying the propagation path of the bacteria in the environment.
   科学家们正在研究细菌在环境中的传播途径。