—What does he want to _____ when he _____ up?
—He wants to be a doctor.

—________ does he want to be a police officer?
—Because he thinks it interesting to be a police officer.

— ________ does he want to be a police officer?
— Because it's interesting.

—_____ does he want to be a police officer?  
—Because it's interesting.

— What does he want _________?
— An actor.