You must know what question you about to search.
Answer:Absence of an enzyme needed to fully digest a food. Lactose intolerance is a common example
Answer: A. Something difficult to understand or define
Explanation: The general definition of elusiveness is "eluding or failing to allow for or accommodate a clear perception or complete mental grasp". This applies to the paragraph because they are saying the path to success is unclear.
A. Citations always go in the late page.