Final answer:
Both age and sobriety affect a person's legal capacity to enter into a real estate contract, as individuals must be legally competent to engage in binding agreements.
Step-by-step explanation:
The legal capacity of a person entering into a real estate contract is affected by both their age and sobriety. Under the law, individuals must have the necessary legal capacity to enter contracts to ensure that the agreements they make are valid and enforceable. This capacity can be compromised if the individual is a minor (age) or if they are not in a sound state of mind, which can be due to a lack of sobriety. Aspects such as contractual rights and property rights are fundamental to entering into agreements about the use of property, and owning the property is essential before you can legally bind yourself or your firm in a contract regarding it.
In conclusion, the correct answer to the student's question is '3) Both A and B', meaning both age and sobriety affect a person's legal capacity when entering into a real estate contract.