external接口指的是外部接口，用来从外部传输文件的接口
例句
1.
Many external influences can affect your state of mind.
许多外在因素都可能影响人的心情。
2.
A combination of internal and external factors caused the company to close down.
内外因结合导致了公司的倒闭。
3.
The state has a duty to protect its citizens against external enemies.
国家有义务保护本国公民不受外敌侵犯。
