Q:

probable or probably? 

In the following sentence, which one is right in the viewpoint of grammatical structure?  Why? 
Notice: In the main source, it is "probable". 

It seems probable that there is no single explanation but that there
  are elements of the truth in several of the hypotheses. 
It seems probably that there is no single explanation but that there
  are elements of the truth in several of the hypotheses. 

A:

Seem is a linking verb and it takes adjective after it. 

e.g It seems probable to ask students to buy a dictionary. 
  You seem happy. 

Probable is an adjective and probably is an adverb

