The answer is a.
An example would be...
my meticulous mother made me miss making meatballs in mexico. :)
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.
They turned and ran when they saw us coming.