Final answer:
Atenolol 100 MG with an expiration date of April 2021 must be used by the end of April 2021. Using it beyond this date is not recommended due to safety and efficacy concerns. The correct option is A.
Step-by-step explanation:
If a bottle of atenolol 100 MG has an expiration date of April 2021, it means that the product should not be used beyond the last day of April 2021. The correct answer to the question "The product must be used by:" is A) April 2021.
After the expiration date has passed, the safety and effectiveness of the medication cannot be guaranteed, and it is generally recommended to dispose of any expired medications.