The correct option is C the
Articles are part of speech, used to indicate nouns and to specify their application. The given sentence requires an article before the musical instrument, violin.
Indefinite articles can be used to express musical instruments as one physical object. For example - I don't have a violin.
However, to express 'violin' as a category of instruments, a definite article must be used. Thus, the correct answer is Option C.
Option D is incorrect, as no article is used when we refer to general ideas, plurals or uncountable nouns.