Fixed grammar and removed unnecessary words: Though Lexie could feel someone sneaking up behind her as she waded through the ball pit, she refused to turn around while searching for her missing brother. The correct placement for the comma is after "pit". Corrected choice: c. after "pit" ✓

Answer: The corrected sentence with the proper comma placement is: "Though Lexie could feel someone sneaking up behind her as she waded through the ball pit, she refused to turn around while searching for her missing brother."

The reason the comma is correctly placed after "ball pit" is because it separates the dependent clause at the beginning of the sentence ("Though Lexie could feel someone sneaking up behind her as she waded through the ball pit") from the independent clause ("she refused to turn around while searching for her missing brother"). The dependent clause cannot stand alone as a sentence and is providing a condition, whereas the independent clause could stand on its own as a sentence.

Extra: In English grammar, commas are used to separate clauses and convey the structure of sentences more clearly. A dependent clause, while containing both a subject and a verb, does not express a complete thought and cannot stand alone as a sentence. An independent clause, however, contains a subject and a verb as well and expresses a complete thought, making it a complete sentence on its own.

Dependent clauses often start with subordinating conjunctions such as "although," "since," "because," "while," "if," or "though." When a dependent clause starts the sentence, a comma is generally placed at the end of the clause, before the start of the independent clause. This helps the reader to pause and understand the separation of ideas. If the independent clause comes first, a comma is typically not needed before the dependent clause. Understanding the correct use of commas helps in writing more clearly and effectively, providing the reader with cues about the structure and meaning of sentences.