Answer:
a
Step-by-step explanation:
This is a fragment because it lacks a subject and a verb. Having a subject and a verb is what a makes a sentence (independent clause) different from a dependent clause.
Dependent clauses, of which a fragment is an example, express ideas, but they do not express them coherently and are often incomplete.
A command sentence is one that gives an order, and a complete thought would be something like:
We enjoy playing beach volleyball and lying on the beach.