This sentence doesn't leave us asking any questions. It expresses a complete thought. We know who - Rick, and we know what - sneezed. Rick is the subject- he is the one the sentence is about. Sneezed is the verb and also happens to be the complete predicate - it not only provides the action in the sentence, but also gives us complete information about the subject.
However, many times it is not enough to just have the subject and verb of the sentence as frequently they do not form complete thoughts. Look at this example:
The car sitting in the garage.
Although it looks like a sentence, this is a fragment. We have a subject - car, and we have a verb - sitting, but, we don't have a complete thought. We are missing the complete predicate, the part of the sentence that tells us everything we need to know about the subject. We are left asking 'what about the car?'.
So, as you can see, it is most important that we ensure that we have enough information to deliver a full thought or expression.
How Can I Correct a Fragment?
Anytime the sentence contains a fragment, corrections must be made. There are three different ways to correct them.
Add a Subject
For instance, if a fragment simply said, 'went to the store', we could fix it by adding a subject. Then, the sentence might say, 'Jose went to the store.' Now, the corrected fragment will become a complete sentence. It has its subject and predicate, and it expresses a complete thought.
Add a Predicate
Let's return to our fragment from above. We need to add a predicate. So, let's take 'The car sitting in the garage' and make it 'The car sitting in the garage is silver.' Now, there is a subject, predicate, and a complete thought. Although the verb part of the predicate, sitting, gave us action, we needed the complete predicate, sitting in the garage is silver, to give us complete information about the subject.
Attach it to a Nearby Sentence
An example of this may be a fragment such as, 'while running around like crazy.' A nearby sentence that it could be added to would be, 'The children were laughing.' After combining, the new sentence would read 'The children were laughing while running around like crazy.' Now that the fragment was added to a sentence, it is no longer a problem.