$A$ is the brother of $B$. $B$ is the brother of $C$. $D$ is the father of $A$. Based on these three statements,which of the following statements cannot be definitely true?

If Kamal says,"Ravi's mother is the only daughter of my mother," how is Kamal related to Ravi?

Pointing to a photograph,a man tells his friend,"She is the daughter of the only son of my father's wife." How is the girl in the photograph related to the man?

All the six members of a family $A, B, C, D, E$ and $F$ are travelling together. $B$ is the son of $C$ but $C$ is not the mother of $B$. $A$ and $C$ are a married couple. $E$ is the brother of $C$. $D$ is the daughter of $A$. $F$ is the brother of $B$. Who is the mother of $B$?

There is a family of six persons $A, B, C, D, E,$ and $F$. They are a lawyer,doctor,teacher,salesman,engineer,and accountant. There are two married couples in the family. $D$,the salesman,is married to the lady teacher. The doctor is married to the lawyer. $F$,the accountant,is the son of $B$ and brother of $E$. $C$,the lawyer,is the daughter-in-law of $A$. $E$ is the unmarried engineer. $A$ is the grandmother of $F$. How is $D$ related to $F$?

Pointing to a person,a man said to a woman,"His mother is the only daughter of your father." How was the woman related to the person?