Which of the followings is true for Merge Sort algorithm?

a$.$ It's time complexity is $O(nlogn)$ since it processes each recursive call in quadratic time.

b$.$ It's time complexity is logn$)$ since it processes each recursive call in constant time.

c$.$ It's time complexity is logn$)$ since it processes each recursive call in linear time.

d$.$ It's time complexity is logn$)$ since it processes each recursive call in logarithmic time.