Doctrine of privity of contract refers to the legal principle that only parties to a contract have the rights and obligations arising from that contract. In other words, a contract cannot confer rights or impose obligations on a third party who is not a party to the contract. The correct answer is option 'A' - a third party cannot sue upon a contract.

Explanation:

1. Understanding the Doctrine of Privity of Contract
The doctrine of privity of contract is a fundamental principle of contract law that ensures that the rights and obligations created by a contract are enforceable only by the parties who have entered into the contract. This means that a third party who is not a party to the contract does not have the legal standing to sue or be sued under the contract.

2. Parties to a Contract
A contract typically involves two or more parties who enter into an agreement with mutual intentions to create legal obligations. These parties are known as the contracting parties or the parties to the contract. They are the only ones who have the legal rights and duties under the contract.

3. Lack of Privity and Third Party Rights
A third party, who is not a party to the contract, does not have privity with the contracting parties. As a result, the third party does not have the legal standing to enforce any rights or obligations arising from the contract. This means that even if the contract directly benefits the third party or if the third party suffers harm due to the contract, they cannot sue the contracting parties for any breach or seek any remedy.

4. Exceptions to the Doctrine of Privity
While the doctrine of privity generally restricts third-party rights, there are certain exceptions recognized by the law. These exceptions include:
- Agency: If the third party is an agent acting on behalf of one of the contracting parties, they may have rights and obligations under the contract.
- Trusts: If the contract creates a trust relationship, the beneficiaries of the trust may have rights and obligations under the contract.
- Collateral Contracts: If a separate contract is made between a third party and one of the contracting parties, the third party may have rights and obligations under that specific contract.

In conclusion, the doctrine of privity of contract states that only parties to a contract have the legal rights and obligations arising from that contract. A third party cannot sue upon a contract unless there are specific exceptions recognized by the law, such as agency, trusts, or collateral contracts.