Please choose the correct answer to the question: A pharmaceutical company develops a new antibiotic to treat pneumonia. After limited testing, the researchers conclude that the antibiotic seems to be effective. How can the researchers strengthen their conclusions?

Answer1: Test the antibiotic on human volunteers. Answer2: Publish their results in a medical journal. Answer3: Ask an independent lab to retest the antibiotic. Answer4: Test the effectiveness of the antibiotic at killing other bacteria.

Answer format: answer1/answer2/answer3/answer4