The binary tree sort implemented using a self – balancing binary search tree takes ______ time is worst case.

The binary tree sort implemented using a self – balancing binary search tree takes ______ time is worst case.
 
(a) O(n log n)
 
(b) O(n)
 
(c) O(n^2)
 
(d) O(log n)
 
I’d like to ask this question from Binary Trees topic in chapter Binary Trees of Data Structures & Algorithms I
 
The question was posed to me at a job interview.