Explanation:
When it comes to suing, a stranger to a contract can only sue if there is consideration involved. Let's break down the components of this statement to understand why the correct answer is option 'B' - Consideration.

Stranger to a Contract:
- A stranger to a contract refers to a person who is not a party to the contract or someone who does not have privity of contract. In simple terms, it means that the person is not directly involved in the contract and does not have any legal rights or obligations under the contract.

Suing:
- Suing refers to the act of taking legal action against someone in a court of law. It is the process of initiating a lawsuit to seek legal remedies or enforce one's rights.

Consideration:
- Consideration is an essential element of a valid contract. It refers to something of value (such as money, goods, services, etc.) that is given by one party to another as part of the contract. Consideration is what makes a contract legally enforceable.

Explanation:
In order for a stranger to a contract to sue, there must be consideration involved. This means that the stranger must have provided something of value to one of the parties to the contract, and that party must have promised something in return.

Consideration is necessary because it ensures that both parties to the contract have exchanged something of value and have made a mutual commitment. It establishes a legal relationship between the parties and provides a basis for enforcing the contract.

Without consideration, a contract may be considered a mere promise or agreement, which is not legally binding. A stranger to a contract cannot sue based on a mere promise or agreement as there is no consideration involved.

Therefore, the correct answer to the question is option 'B' - Consideration. It is the presence of consideration that gives a stranger to a contract the legal right to sue in a court of law.