Answer:
B. to
It never occurred to me to ask him for proof of identity.
Explanation:
To occur to (someone) is a phrasal verb that means to come into someone's mind.
Phrasal verbs are verbs that consist of the main verb and an adverb or a preposition, or both. Usually, we can't determine their meaning just based on what these words mean individually. For example, the verb to occur means to happen, while to has many meanings and can function as a preposition, adverb, and the infinitive marker. This knowledge doesn't help us determine what the phrasal verb to occur to means, though.
