Answer :
It is C. Compound sentence. This is because it is far from simple, and even thought it might seem as a run on sentence, it is not, as run on sentences are sentences connected with a comma, yet this one is connected with a semi-colon, which is a correct way of connecting sentences.
A simple sentence contains the basic element
that make a sentence and that is a subject and a predicate. The sentence must
one independent clause and expresses one idea. Compound sentences other hand contains
two ideas. In the sentence: My sister works with clay; she
molds and paints it. It is a compound sentence since there are two ideas, that
is, two subject ‘sister’ and ‘she (basically still the sister)’ and two
predicates ‘works with clay’ and ‘molds and paints it’.