Subjects and verbs must agree in number. This is the cornerstone rule that forms the background of the concept. The dog growls when he is angry. The dogs growl when they are angry. Don’t get confused by the words that come between the subject and verb
ELA creative writing outlaw The Seven Deadly Sins of Punctuation And How You Can Avoid Them (Note: Read carefully. They preface each "faux pas," telling you the correct usage, but provide the WRONG way as examples. It's confusing).