请问这个定语从句中的谓语在哪里
The professor can hardly find sufficient grounds on which to base his argument in favor of the new theory.在这个句子里面有个定语从句,on which to base his argument in favor of the new theory.在这个定语从句中,to base 是接在哪里,这个定语从句中没有谓语?to base 是什么结构?