Mum or Dad?

Dad: Who do you like more, Mum or Dad?
Son: Both.
Dad: Ok if I go to America and your mum goes to Paris, where will you go
Son: Paris
Dad: That means you like your mum more?
Son: No, I like Paris.
Dad: OK, if I go to Paris and your mum goes to America, where will you go
Son: America.
Dad: [angry] Why!?
Son: 'cos I've been to Paris before!