The following answers use correct punctuation: (a) Dear Ms. Collin: When the error message appears on the screen, you should exit the program, right. (b) When you leave at 5:00 p.m., please shut the door and lock it; however, do not set the alarm.
In sentence (c) the punctuation in 1980's is not correct. It is a common mistake to include apostrophes when pluralizing a number or an abbreviation. Apostrophes are generally used in contractions and to indicate the possessive case.
