Explanation:

- Age of the parties: A person must be of legal age, usually 18 or above, to enter a valid contract.

- Soundness of mind of the parties: A person must have the mental capacity to understand the contract terms and consequences.

- Intelligence of the parties: Generally not a standard requirement for contract competency. It's mostly about understanding terms rather than overall intelligence.

- Both (a) and (b): Combines the age and mental capacity requirements, making it more comprehensive.

Correct Answer: Option 3: Both (a) and (b)

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