middle vacuum

• 空中

middle vacuum的用法和样例：

例句

1. Sound can not be conveyed in a vacuum.
   真空中声音无法传播。
2. Sealed inside a glass tube, a stream of electrons carried a current through a vacuum between electrodes.
   在一个密封的玻璃管内，带电的电子流在两电极间的真空中流动。