How do you ask the order or the position in the sequence of people or things?
For instance,in the conversations below, with what questions do you fill in ( ) ?

A : "How many brothers and sisters do you have?"
B : "7."
A : "( )?"
B : "I'm the third oldest among us."

C : "What's the longest river in the US?"
D : " The Mississippi River."
C : "( )?"
D : "It's the 4th longest river in the world."

E : "Who's the current president of the US?"
F : "Barack Obama."
E : "( )?"
F : "He's the 44th President of the US."