Researchers mixed a kind of plant lactic acid bacteria into the experimental rat's feed. After the experimental rat consumed this feed for 4 weeks, it continued to exert mental stress enough to cause sleep disturbance for two weeks, and then let the experimental rat pedal during the night activity period. The results showed that the downward trend of the activity of the experimental mice after extracting the lactic acid bacteria was restrained, while the control group of rats that did not consume the feed containing the lactic acid bacteria had difficulty falling asleep during the day and lack of sleep, resulting in a significant decrease in their night activity. Therefore, researchers believe that the ingestion of lactic acid bacteria can improve sleep disorders caused by mental stress. Which of the following, if true, would most challenge the above conclusions? ['Lab rats usually sleep during the day and come out at night.', 'The expression of a gene related to sleep disorders is suppressed in experimental mice from which lactic acid bacteria are extracted.', 'The composition of the plant lactic acid bacteria is inconsistent with most lactic acid bacteria.', 'except for the runner, there is no other activity in the rat at night.']