Explanation

The answer is None of these, because if M's father is T's grandfather's son, then M is T's cousin. 

Here is the breakdown of the relationship:

T's grandfather's son is either T's father or T's uncle.

The problem states this person is M's dad.

If the son is T's father, then M is T's son.

However, if T's father is M's dad, it would mean that T's father is also M's father, which is a contradiction.

If the son is T's uncle, then M is the child of T's uncle, making M T's cousin.