The question tells us that "you" are going to do shopping, so we want to say " I am going..." and can start with finding the form for "I am going" - yo (I) voy (voy is first person singular of "ir" to go).
And this is already enough to answer the question, as there is only one option with "voy" - so the correct answer is:
C) Voy de compras al tianguis
