The answer to your question would be that the underlined word that functions as a preposition is <em>of.</em>
Explanation:
The only preposition in the sentence above is <em>of.</em> <em>Machines</em> is a noun, <em>have</em> is functioning as an auxiliary verb. Have + <em>come and gone</em>, behaving as the main verbs form the present perfect tense. Then, <em>but</em> is a conjunction, <em>the </em>is the definite determiner, <em>spirit</em> is a noun as well as <em>invention</em>. Finally, <em>lives</em> is a verb and <em>forever</em> an adverb.
they need be smart and they should be able to go around and help the students when they need help and they should have and extra set of pencils cause you now how you always be breaking them if you actually at school