我本打算去他的派对，但我生病了。

I was going to go to his party, ___but I was ill.

很抱歉这么久没写信，但我上周非常忙。

I'm really sorry I haven't written for so long, ___but I was very busy last week.

他计划去徒步，但下了一整天的雨。

He planned to go hiking, ___but it rained all day.