periodical backup的用法和样例：
例句
- The system includes a backup auxiliary system.
此系统还有一个后备的辅助系统。 - In local backup relaying, faults are cleared locally in the same station where the failure has occurred.
在近后备继电器中，故障在失效已经发生的相同的地方被地切除的。
词汇搭配
- back up (因积聚而)拥堵...
