I've sent him a letter _____ him to the party on the Sunday.(邀请)

问题描述:

I've sent him a letter _____ him to the party on the Sunday.(邀请)
填什么?为什么?

填 inviting.
如果填invite的话,前面要加to.现在句中没出现to,所以只能填inviting,表示动名词.
意思是对这封信函的解释,而并不作动词使用.