He said he would go swimming ___________ the rain.

He said he would go swimming BUT FOR the rain.

他说，要不是下雨了，他就会去游泳！

but for或者except for
都是一个意思，表示“除了”

他说，他会去游泳除非天下雨了。

He said he would go swimming -except for- the rain.

in
难道就不能在雨中游泳吗?
如果这句话的意思是如果下雨就不去游泳的话,那么你再考虑楼上的吧

but for