Which of the following is not a complete sentence?

The selection that is not a complete sentence is indeed the option that describes "Working far into the night in an effort to salvage her little boat." This phrase lacks a subject and a main verb, which are essential components of a complete sentence. It begins with a gerund ("Working") and functions as a noun phrase, but it does not convey a complete thought or stand alone.

In contrast, the other options are all complete sentences: they each contain a subject and a predicate, conveying a full idea. The first option presents a clear conflict and outcome, the second details an action taken by a subject, and the third communicates a future event clearly. Each of these sentences can stand alone as meaningful statements, which is what differentiates them from the option describing "Working far into the night."