In 1870, Clavin, along with Adirondack hunter Alvah Dunning, made the first known ascent of Sweard Mountain, _______ far from roads or trails.

A remote peak

The sentence has a main subject and verb with several phrases and commas. One should identify Calvin and made... as part of the main sentence. After the blank we have a phrase which leads to give extra information on the mountain. This means we need the first part of the phrase. 1. It is not (D) because the connector it has requires the phrase to have a verb of its own, and it doesnt. 2. It is not (C) because it has a verb and would require a connector. 3. It is not (B) because it has a subject and verb and no connector as an adjustment. 4. It is (A).