Concept:The correct past participle of the verb "grind" is needed after "should have".Explanation:The sentence "should have" must be followed by the past participle form of the verb.The verb "grind" has the forms: grind, ground, ground.Thus, the past participle is "ground".It is not "grind", "grinds", or "grounded".So "ground" fits the blank correctly.Answer:A. ground