Q: You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each 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?
(A) Test the antibiotic on human volunteers. (B) Publish their results in a medical journal. (C) Ask an independent lab to retest the antibiotic. (D) Test the effectiveness of the antibiotic at killing other bacteria.
A:
C