What is a short sequence of characters that appears at the end of a filename and is preceded by a period called?

The short sequences of characters that appear and can be seen at the end of a filename preceded by a period is filename extensions. While a sequence structure is a set of statements that execute in the order they appear. 

answer; the correct answer is conflict- related aggression; +

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.