For a few minutes he tapped the switch after each flash, on average every six seconds.

最初几分钟，每闪一次他揿一下按钮，平均每六秒钟一次。

youdao

For a few minutes he tapped the switch after each flash, on average every six seconds.

最初几分钟，每闪一次他揿一下按钮，平均每六秒钟一次。

youdao