Note: This question appears to be incomplete in the provided text. The question stem is cut off and no options are provided. In a complete question about investment bank trading profits, the correct answer would typically relate to market-making activities where the bank buys and sells securities for its own account, earning profits from bid-ask spreads and price movements. Common scenarios include:

• Market making - buying from sellers and selling to buyers at different prices
• Proprietary trading - trading for the bank's own account
• Arbitrage - exploiting price differences between markets

Without the complete question and options, this explanation covers the general concept of how investment banks earn trading profits.