Final answer:
The punctuation mark that enhances clarity in a sentence about successful dieters is a semicolon if the sentence contains two related independent clauses. A semicolon is effective when the clauses are closely related or when the second clause restates the first.
Step-by-step explanation:
The question asks which punctuation mark would enhance clarity in a sentence about successful dieters. To determine the correct punctuation, one should consider the rules and purposes of different punctuation marks. A period ends declarative or imperative sentences and is used to mark the end of a statement. A comma is often used to separate items in a list or to set off clauses and phrases within a sentence. A semicolon is used between two independent clauses that are closely related in meaning, which can be particularly effective if the second clause restates the first or adds related information. An exclamation mark is used to express strong emotion.
Based on these uses, if the sentence in question is a compound sentence with two related independent clauses, a semicolon would be the best choice to enhance clarity.