Answer:
d. is not a contract principle
Step-by-step explanation:
Contracts have to be voluntary, and legal. In other words, the contracting parties have to voluntarily agree to the terms of the contract, and the goal of the contract must be legal under the specific set of laws that apply.
If there is no voluntary consent from one of the parties, there is not a contract. The contract is void, null, and cannot be enforced.