$641$ point

Cindy, a real estate agent, sells her friend Doug's house without charging a commission. In return, Doug promises to give Cindy $$1,000.$ This promise is not an enforceable contract because

selling the house was the agent's preexisting duty.

the promise of a payment of $$1,000$ is illusory.

selling the house was a foreseen difficulty.

the house has already been sold$-$the consideration is past.