Which of the Following Considerations Is Legally Insufficient

Which of the following considerations is legally insufficient?

A) Tony bought a book for $100. Ruby offers to buy it for $10.
B) Tony bought a book for $100. He offers to sell it for free if Ruby helps him in shifting to his new house.
C) Tony bought a book for $1,000. Ruby offers to buy it for $2,000 if it does not rain the next day.
D) Tony bought a book for $100. He offers to sell it to Ruby for free if she helps him befriend the new girl in their lane.
E) Tony bought a book for $1,000. He offers to sell it to Ruby for $10 if she quits drinking.