The question is. A multiple choise 
" i dont think you have any real cause ....complaint.
Choices ( of / for/ with /on) 
Clearly it"s either of or for 
In my model answer it should be "for" 


2" revenge was the main ....the fire .
Choices ( reason for . Cause of . Reason of )
It should be " reason for" 

There must be a difference between cause and reason in their usages
And also prepositions ???