Haj Promises to Transfer to Johnny a Jukebox Worth $1000

Haj promises to transfer to Johnny a jukebox worth $1000.Which of the following is not valid consideration for Haj's promise?

A) Payment by Johnny of $50 cash for the jukebox
B) The transfer by Johnny to Haj of Johnny's car worth $3000
C) A promise by Johnny to mow Haj's lawn every month for a year
D) A promise by Johnny to buy something nice for Haj in return