This question is about identifying the term for a specific type of verb construction. The correct answer is 'A. Phrasal verb' because it refers to a verb that is combined with a preposition to create a new meaning, and these cannot be separated. Option B is incorrect because a gerund is a verb form that functions as a noun. Option C is incorrect because an infinitive is a verb form that typically indicates purpose or intention. Option D is incorrect because a particle is a word that is used with a verb to create a phrasal verb, but it is not the term for the fixed expression itself.