#1 is correct. Short sentences don't flow smoothly as longer sentences do, so the abruptness of a short sentence in a middle of a written work will add intense contrast placing emphasis on the statement.
#2 is incorrect because short sentences can be used effectively to add emphasis to a statement. This use of short sentences often strengthens the author's message and actually can help reveal a writer's skill.
#3 is incorrect because if we combine a short sentence with another short sentence, it's no longer a short sentence. This obviously defeats the entire purpose of an abrupt sentence.