'Began' is a past tense form of a verb and 'preparing' is a gerund (a noun formed from a verb).

In the sentence "They quickly began preparing breakfast," the words "began" and "preparing" are both verbs. Here's a breakdown of their parts of speech and their roles in the sentence: "Began": Part of Speech: Verb Role in the Sentence: "Began" is the main verb of the sentence. It indicates the action that "they" (the subject) initiated. In this case, the action is starting the process of preparing breakfast. "Preparing": Part of Speech: Verb (specifically, it is a gerund) Role in the Sentence: "Preparing" is also a verb, but it's functioning as a gerund in this sentence. A gerund is a verb form that acts as a noun. In this sentence, "preparing" is the direct object of the verb "began." It answers the question "What did they begin?" The answer is "preparing breakfast." So, "preparing" is a gerund that serves as the object of the verb "began." In summary, both "began" and "preparing" are verbs in this sentence, but "preparing" is a gerund acting as a noun, specifically as the direct object of the verb "began."