To properly represent the relationship "Man has a best friend who is a Dog", we need to use composition to indicate that a Man object has a Dog object as its best friend.

Now, let's go through each option and explain why it is right or wrong:

A. class Man { private Dog }

This option is incorrect. The syntax used to represent the relationship between Man and Dog is incorrect. The "" does not make sense in this context.

B. class Man { private BestFriend dog; }

This option is incorrect. Although the variable name "dog" is used, it does not represent the intended relationship. The class BestFriend is not defined anywhere and doesn't make sense in this context.

C. class Man { private Dog bestFriend; }

This option is correct. The class Man has a private variable named "bestFriend" of type Dog, indicating that a Man object has a Dog object as its best friend.

D. class Man implements Dog { }

This option is incorrect. The interface Dog cannot properly represent the relationship between Man and Dog, and implementing the Dog interface does not make sense in this context.

Therefore, the correct answer is:

The Answer is: C. class Man { private Dog bestFriend; }