Final answer:
Managers typically check the shelf life of products in a vending machine regularly according to company policy to ensure product quality and safety; however, there is no standard frequency that applies to all cases.
Step-by-step explanation:
The frequency at which managers are required to check the shelf life of products in a vending machine typically depends on the policies of the company operating the vending machines and the types of products offered. While there is no universal rule for all vending machines, a general best practice would be to check them more regularly than monthly to ensure product quality and consumer safety.
However, answering the student's original multiple-choice question requires additional context as regulations and practices may vary by jurisdiction and company policy. Without specific guidelines from a regulating body or the company's standard operating procedures, there is no definitive answer. A responsible manager should always ensure that all products are within their expiration dates to provide safe and high-quality products.