When do you use a comma in a sentence

It's to know your purpose before you read something because a purpose can:

Which best explains how this excerpt creates suspense it develops the plot using dialogue instead of description. it explains that the fishermen have found two graves on the island. it shows that manjiro is a character who asks a lot of questions. it includes a question that the reader will want to know the answer to.

Which type of pronoun clearly shows what is being referred to a specific person place or thing