Which sentence requires a comma for correct punctuation?

The sentence that requires a comma for correct punctuation is the one referring to the visit to the campus. In this case, a comma is needed after the introductory phrase "Before touring the campus." The purpose of this comma is to clarify the sentence structure and enhance readability. When an introductory clause or phrase precedes the main clause, a comma should generally follow it to indicate a pause and prevent misreading.

In the context of the other sentences, they do not require a comma to be grammatically correct. The second sentence lists activities without a necessary conjunction, which is handled by using commas to separate the items. The third sentence appropriately uses a comma after the introductory phrase "On Saturday," which already adheres to correct punctuation practice. The fourth sentence also correctly places a comma after the introductory conditional clause "If you need help," leading to clear and effective communication.