Answer:
Option B is the best way to write the underlined parts of sentences 2 and 3.
Sentence 2: They have a special finish that helps.
Sentence 3: The finish helps the swimmer glide through the water.
Option B provides a clear and concise way to connect the two sentences and convey the idea that the special finish of the swimsuits helps the swimmer glide through the water. It avoids any ambiguity or redundancy in the language.