Functions of all verbs in sentence: You must be 18 years old to drive a car.

[Kawkabwaheed]

Greetings:
In the sentence: "You must be eighteen years old to drive a car.", I know that "must" is the helping verb. However, what grammatical labels and functions can I attend to the verbs "be" and "to drive" in this sentence? Any help with question is greatly appreciated.

[Mister Micawber]

.
'Be' is the main verb; it is a linking verb.
'[in order] to drive a car' is an adverbial (an infinitive clause, or a prepositional phrase if you accept my inserted words)
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Native English teacher at Mister Micawber's