The answer is likely C) Gerund. A gerund is a noun that ends in -ing, essentially turning a verb into a noun. Conversely, the present participle is a progressive verb ending in ing that functions as a noun. In order to know for sure, consider the context.
Example of a gerund:
His walking has really improved. Ice-skating is his favorite sport.
Example of a present participle:
What are you doing? I am walking to school.