Check My Work $(1$ remaining$)$

Crist$$bal recently purchased a new Ford F$150$ pickup truck and is now trying to sell his used truck with $180,000$ miles on the odometer on eBay. He has created a listing including photos, and he decides to use eBay's "Buy It Now" feature rather than an auction. The truck has been listed for several weeks, but so far no one has contacted him about it$.$ Which condition of exchange most directly relates to Crist$$bal$\text{'}$s eBay listing for his truck?

a$.$ Each party has something that might be of value to the other party.

b$.$ Each party believes it is appropriate or desirable to deal with the other party.

c$.$ There must be at least two parties.