Barbara is taking biology 1 next year, and she and joe agree that he will sell his used biology book to her for $25. they agree that payment and delivery will take place next week. after making his agreement with barbara, joe saw one of his friends, tom, who also is taking biology 1 next year. tom agreed to pay $30 for the biology book, and joe agreed. barbara found out joe sold the book to tom from a reliable source before she had paid for the book and before joe had delivered it to anyone.

a. joe's offer to barbara is revoked.

b. joe has a contract with tom, but not with barbara.

c. joe’s offer to tom was invalid for a contract to be formed.

d. none of the above.