How are gerunds similar to infinitives? a. they both are examples of irregularly conjugated verbs. b. they can both function as adjectives. c. they can both function as nouns. d. the both need auxiliaries.

The correct option is this: THEY CAN BOTH FUNCTION AS NOUNS.
A gerund is a noun that is made from a verb by adding 'ing' to it. It functions as a noun.  An infinitive is a base form of a verb with 'to'. Infinitive usually functions as a noun, although it can also function as an adjective and an adverb. 

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