Which of the Following Is an Example of a Valid

Which of the following is an example of a valid contract?

A) Tom offered to clean Harry's garden for a sum, which Harry did not agree to. On a Sunday afternoon, Tom asks Harry to pay $20 for cleaning the garden, which Harry refuses.
B) Tom offered to clean Harry's garden for a sum. Harry was very drunk and agreed. On a Sunday afternoon, Tom asks Harry to pay $20 for cleaning the garden, which Harry refuses. After persistent requests by Tom, Harry agrees to pay $10, which Tom declines.
C) Tom offered to clean Harry's garden to which Harry agreed. On a Sunday afternoon, Tom asks Harry to pay $20 for cleaning the garden, which Harry refuses.
D) Tom and Harry bet on the ongoing FIFA match, on losing which Tom had to clean Harry's garden. On a Sunday afternoon, Tom asks Harry to pay $20 for cleaning the garden, which Harry refuses.
E) Harry calls up Tom asking him to clean his garden. He offers $20 for the job and tells him that Tom can have free lunch thereafter for the next two weeks at his place. Impatiently, Tom cuts him off and agrees to clean the garden on whatever terms Harry wants.