P, Q, R, S, T and U are six members of a family. R is the spouse of Q, U is the mother of T and S is the daughter of U. P's daughter is T and R's son is P. There are two couples in the family. Which one of the following is correct?

Let's construct the family tree based on the given information:

1. "R is the spouse of Q" -> Q - R (Couple 1)
2. "R's son is P" -> P is the son of R and Q. So, Q - R | P (male)
3. "P's daughter is T" -> T is the daughter of P. So, Q - R | P (male) | T (female)
4. "U is the mother of T" -> Since P is the father of T, U must be the spouse of P. So, Q - R | P (male) - U (female) (Couple 2) | T (female)
5. "S is the daughter of U" -> S is also the daughter of P and U, making S and T siblings. So, Q - R | P (male) - U (female) | T (female), S (female)

All 6 members (P, Q, R, S, T, U) are present, and there are two couples (Q-R and P-U).

Now let's evaluate the options:

A) Q is the grandfather of T Q is a grandparent of T. However, we don't know Q's gender. Q could be male (grandfather) or female (grandmother). So, this is not definitively correct.

B) Q is the grandmother of T Similar to A, we don't know Q's gender. Q could be male (grandfather) or female (grandmother). So, this is not definitively correct.

C) R is the mother of P R is a parent of P. We know R's son is P, but R's gender is not specified. R could be male (father) or female (mother). So, this is not definitively correct.

D) T is the granddaughter of Q From the tree, Q is a grandparent of P, who is the father of T. Thus, Q is a grandparent of T. T is explicitly stated as P's daughter, meaning T is female. A female grandchild is a granddaughter. Therefore, T is definitely the granddaughter of Q, regardless of Q's gender. This statement is definitively correct.

The final answer is D