Final answer:
The best correction for Sentence 1 'Dear students' is to add a comma, making it 'Dear students,' to correctly separate the salutation from the rest of the sentence.
Step-by-step explanation:
The best correction to make to Sentence 1 which reads "Dear students" would be option A, which adds a comma after the salutation 'students'. The comma is necessary as it separates the salutation from the rest of the sentence, following standard English punctuation rules for direct address. Therefore, the corrected sentence should read: "Dear students,". When starting a letter or an email, it is customary to use a comma or a colon after the salutation, and in more informal contexts, a comma is more commonly used.