gerund vs infinitives

Answer B shows that the action of possessing more fingers than usual happened in the past - there is no reason for past tense since the question gives a definition which is always true and not a thing of the past
Answer A doesn't seem correct as the noun "numbers" is in plural unnecessarily - Are you sure that A is the OA?
Answers D and E - sound incorrect because of the awkward construction "to have....is....."
Answer C seems correct - it uses the v-ing form as the subject and the noun "number" is in singular