None of the banks you mentioned can be short. Only China Bank in Shanghai has margin foreign exchange business, while China banks in other regions do not. When trading online, these banks can trade 24 hours a day and entrust stop-loss orders. Transaction costs are spreads, and the spreads of banks vary from place to place and are not completely unified. Generally, the bid-ask spread of a firm offer is about 30 points, and the margin is about 10 points.