Answer:
D. They suggest the narrator is not fully responsible for the outcome of his story.
Because Radley is much older than them, and Scout, Jim, and Dill find him interesting because of this.
The sentence that contains a boldface infinitive is D. Lisa wants TO GO.
It is easy to spot an infinitive - it is usually a combination of the word TO plus a verb.
A and C are incorrect because those are not infinitives, but rather prepositional phrases. B is incorrect because it is an infinitival phrase, rather than a single infinitive.
