Which of the Following Is a Valid Contract According to Common

Which of the following is a valid contract according to common law?

A) Jon offers to sell his car to Jack for $50,000 and promises to keep the offer open for 10 days. Jack offers to pay him $1,000 extra for keeping the offer open for 20 days. Two days later, Jon calls Jack to revoke the offer but Jack misses his call. Jack calls up Jon on the ninth day to accept the offer.
B) Jon telephones Jack to tell him about selling his car to Jack for $50,000. He promises to keep the offer open for 10 days. Two days later, Jon telephones Jack to revoke the offer. Jack telephones Jon on the ninth day to accept the offer.
C) Jon offers to sell his car to Jack for $50,000 and promises to keep the offer open for 10 days. Jack calls up Jon on the fifth day accepting the offer and on the tenth day goes to buy the car. Jon asks for $55,000.
D) Jon offers to sell his car to Jack for $50,000 and promises to keep the offer open for 10 days. Two days later, Jon sends a telegram to Jack to revoke the offer. On the morning of the fifth day Jack receives Jon's telegram. Jack calls up Jon the same afternoon accepting the offer.
E) Jon offers to sell his car to Jack for $50,000 and promises to keep the offer open for 10 days. On the third day Jack calls up Jon, declining the offer. On the tenth day, Jon asks Jack to come and buy the car at the agreed price.