Complete sentences

A complete sentence MUST have both a subject and a verb. In other words, there must be a "something/someone" in your sentence that is doing something. You can't have an action that isn't attached to an actor, or vice versa.

Complete sentence: Jack woke up at 6am.

"Jack" is the subject, "woke" is the verb.

Fragment: Because of the snow.

There is not an verb in this sentence, so it is not complete.