The correct answer is: A. Optimistic : Pessimist
Pusillanimous means cowardly, while dastard means a cowardly or despicable person. Optimistic means having or showing a hopeful and confident attitude, while pessimist means a person who tends to see the worst in things.
The other options do not have the same relationship as the original pair of words. Magnanimous means generous or forgiving, while misanthrope means a person who hates or distrusts all people. Plebeian means of or relating to the common people, while entrepreneur means a person who organizes and operates a business or businesses, taking on greater than normal financial risks in order to do so. Impecunious means having little or no money, while mendicant means a beggar.