Select the best punctuation mark for the blank in the following sentence.
After standing in the rain for nearly half an hour _________ Dawn decided she was not going to wait on Mike any longer.

In this sentence, the word “after” is a common starter word for the introductory clause and should be followed by a comma. A clause is a group of words that contain both a subject and a predicate and help to form a sentence. Other common starter words that require a comma after the introductory clause include when, while, although, and since.