Final answer:
The correct answer is that the provision stating the buyer must make monthly payments by a specific date can legally be included in an Illinois installment contract. This is a standard term to ensure sellers receive timely payments.
Step-by-step explanation:
The question pertains to provisions that can legally be included in an Illinois installment contract regarding property sale. Among the given options, C) The buyer must make monthly payments by a specific date is a legal provision that can be included in such a contract. This stipulation ensures that the seller receives timely payments for the property. This expectation is a common term in real estate installment contracts. Options A), B), and D) may not be legally enforceable as they can violate the rights of the buyer or not adhere to required legal processes such as notice before repossession.