If P % Q means P is the brother of Q, P ! Q means P is the mother of Q and P * Q means P is the son of Q, then which of the following shows that C is F's mother's brother's son?

We need an expression that states C is the son of F's mother's brother (maternal cousin).
Let's analyze option C: *C D % E ! F**

Breaking down from right to left:

1. $E!F\to$ E is the mother of F.
2. $D\%E\to$ D is the brother of E. (Since E is F's mother, D is F's mother's brother).
3. $C\ast D\to$ C is the son of D.

Combining these facts together, C is the son of D (who is F's mother's brother). This means C is F's mother's brother's son.
Thus, option C is correct.