When drafting a contract, Jonathan and Drew should focus on principles that ensure the agreement is valid and enforceable. The key principles they should remember are:
B. Exchange of value; offer and acceptance
These principles are foundational to contract law. "Offer and acceptance" refers to the mutual agreement between parties, where one party makes a proposal (offer) and the other agrees to it (acceptance). "Exchange of value" signifies that something of value is being exchanged between the parties, which is necessary for a contract to be binding.
While the other options contain important elements related to contracts, B directly addresses the core principles that constitute a valid contract.