Please choose the correct answer to the question: In a lab investigation, students use Brand X batteries in a flashlight and Brand Y batteries in a radio. After two hours, the flashlight stops working, but the radio continues to work. As a result, the students conclude that Brand Y batteries last longer. Which statement about the conclusion of the investigation is most accurate?

Answer1: The conclusion is valid because they tested two different brands. Answer2: The conclusion is invalid because the test had multiple variables. Answer3: The conclusion is valid because they conducted the investigation in a lab. Answer4: The conclusion is invalid because the real names of the batteries were hidden.

Answer format: answer1/answer2/answer3/answer4