后面不加介词。

去国外，出国

We can't afford to go abroad this summer.

今年夏天我们没有足够的钱去国外。

Every time I go abroad， I have to struggle with jet lag.

我每次出国都要费力地倒时差。

We always go abroad in the summer.

我们总是在夏天去国外。

He often has to go abroad for work.

他经常去国外出差。