9) what is the best description and explanation for the underlined words in this sentence? to dance was everything. a) to dance is an infinitive verb form functioning as a noun. b) to dance is an infinitive adjective form functioning as a noun. c) to dance is an infinitive adjective form functioning as a verb. d) to dance is an infinitive noun form functioning as an adjective

The correct answer is A. To dance is an infinitive verb form functioning as a noun. 
The infinitive form to dance in the sentence above is used as a subject of a sentence. Given that the subject can only be a noun, we can deduce that C and D are incorrect. B is incorrect because the infinitive is not in the adjective form, but rather in the verb form functioning as a noun/subject in the sentence.