Plutonium is trading at a one-year futures price of $5,000 per gram. A futures contract comprises 100 grams. The initial margin is $100,000 and the maintenance margin is $80,000. You are short one futures contract. There is a margin call when the price per gram of plutonium changes to (a) $4,750 (b) $4,900 (c) $5,100 (d) $5,250