方法：用真空负压表、延迟控制线路，接通电话机免提键、存储拨号键。

Methods The vacuum negative pressure meter and the delayed control line were used.

youdao

方法：用真空负压表、延迟控制线路，接通电话机免提键、存储拨号键。

Methods The vacuum negative pressure meter and the delayed control line were used.

youdao