A trader is long four July gold futures contracts, each with a contract size of 300 oz. If the price of July gold increases from $380.20 to $381.00 per ounce the change in the margin balance will be :

A．

B．

C．

用止血带止血时，扎紧止血带以刚使肢端动脉（）为度。上肢每60min，下肢每80min放松一次，每次放松（）。