Final answer:
Without access to specific course enrollment information, it is not possible to accurately determine which individual is taking the Environmental Law and Business course on Apex.
Step-by-step explanation:
The question 'Who is taking Environmental Law and Business on Apex?' does not provide enough context for an accurate, factual answer, because it appears to be a question specific to the individuals within a particular class or course offering. This question could be related to any number of scenarios in which a student or group of students are enrolled in an Environmental Law and Business course on the Apex learning platform. Since this information is not publicly verifiable and is likely private to the group or class, it is not possible to accurately state whether John, Mary, Sarah, or David is taking the mentioned course without access to the course's enrollment list or further context.