In which sentence does the underlined adverb clause modify an infinitive?

in the northern atlantic, where the titanic sank, large icebergs are common during cold months.

we wanted to visit the museum while it was featuring a traveling exhibit about the titanic.

although the titanic sank to the ocean floor, explorers recovered some artifacts from the wreck.

We wanted to visit the museum while it was featuring a traveling exhibit about the Titanic.

Explanation:

The adverb clause while it was featuring a traveling exhibit about the Titanic modifies the infinitive to visit.

There are no infinitives in the other sentences.

We wanted to visit the museum while it was featuring a traveling exhibit about the Titanic.

Explanation:

Adverb is the grammatical class of words that modifies a verb, adjective or other adverb. Never modify a noun. It is the invariable word that indicates the circumstances in which the verbal action occurs.  The adverbial clauses have the same function as an adverb.

On the basis of this we can conclude that the adverbial clause "while it was featuring a traveling exhibit about the Titanic." is modifying the infinitive verb "to visit". Moreover, this is the only phrase among those that were shown in the question, which has a verb in the infinitive form.