Final answer:
When a BD lends stock to another BD, the borrower usually sells the stock.
Step-by-step explanation:
When a BD lends stock to another BD, the borrower usually sells the stock. This is because when a BD lends stock, it is typically done through a process called securities lending, where the borrower pays a fee to the lender in exchange for the temporary use of the stock. The borrower then sells the stock in the market to generate profit or meet specific investment needs.