Final answer:
John is accountable for the computer purchase made by his son because he ratified the contract through his conduct of using the computer for several weeks.
Step-by-step explanation:
In the described scenario, the correct answer is D) ratified the purchase by John's conduct. By using the computer for several weeks without objection, John implicitly ratified the contract his son made on his behalf. John's son purchased a computer in John's name without being authorized. When John learned about this, he sternly rebuked his son but continued to use the computer for several weeks. After losing interest in the computer, John offered to return it, claiming that the purchase was unauthorized. Ratification can be express or implied, and in this case, it's implied by John's actions after learning about the purchase. Even though John initially rebuked his son, continuing to use the computer constitutes acceptance of the benefits of the contract, which is a form of ratification.