Which term correctly identifies the underlined words in the sentence?

When books have tiny print, the words are difficult to read.

A.

participle

B.

participial phrase

C.

infinitive

D.

infinitive phrase

I would disagree. To read would be considered an infinitive. The reason why I think the answer is infinitive is because, I know in Spanish, which is similar to English, to do something (to read) it was always considered an infinitive. It's an action verb. It's not d because there are no other words following the to read. Hopefully this makes more sense.