Figure below is a balanced binary tree. If a node inserted as child of the node R, how many nodes will become unbalanced?

Figure below is a balanced binary tree. If a node inserted as child of the node R, how many nodes will become unbalanced?
 
(a) 2
 
(b) 1
 
(c) 3
 
(d) 0
 
The origin of the question is Binary Trees topic in chapter Binary Trees of Data Structures & Algorithms I
 
This question was addressed to me by my college director while I was bunking the class.