Answer:
C
Step-by-step explanation:
Proof by some contradictions:
D is not a good example because she does not pay anything upfront
B is not a good example because he pays <u>everything </u>upfront with some of the money from a third party
A is not right because the 500 is a security deposit, which is a different concept from a down payment
Therefore the answer should be C, where money is payed upfront and payed after he receives the product.