external sheath

例句：

1. 1. The robot's external sheath is made of tough plastic.
   这个机器人的外层护套是由坚固的塑料制成的。
2. 2. The scientist used a microscope to examine the external sheath of the virus.
   科学家使用显微镜检查病毒的外层护套。
3. 3.The engineer designed an external sheath that could withstand high temperatures.
   工程师设计了一个能够承受高温的外层护套。