Porter's 5 Forces question into, difficult, therefore, question, industry

spartan1

If an analyst was assessing a pharmaceutical company’s competitive strategy, the length of the drug patent would be related to which of Porter’s Five Forces?
A) Threat of new entrants (Entry barriers).
B) Bargaining power of buyers.
C) Rivalry among existing competitors.
Your answer: C was incorrect. The correct answer was A) Threat of new entrants (Entry barriers).
Long drug patents make entry into the industry difficult; therefore this relates to barriers to entry.
—-
question: why can’t the answer be A? a patent would have separate you from your competitors and thus decrease the rivalry…no?