Answer:
C. Penicillin, one of our most important drugs, comes from mold.
Explanation:
A is wrong because the verb is in an incorrect form. The noun here 'penicillin' is singular, so the verb should be plural (or present tense, as <em>comes</em>) to agree with the noun.
B is wrong because the drug here is penicillin, but the sentence structure and comma placement make it seems as though the drug is 'mold', which comes <em>from </em>penicillin.
D is wrong because the verb here is in present continuous tense, <em>coming</em>, which disagrees with the statement.
C is right because the verb tense is present, and plural, <em>comes</em>, and agrees with the statement.
