A house is the most expensive thing most people will ever buy. Very few people have enough money of their own to buy a home, so they have to borrow money from a bank. Borrowing money from a bank to buy a house is called "take a mortgage (抵押)." The bank usually lends money or gives a mortgae for twenty-five years. Houses are so expensive that many people nowadays have to borrow as much as $ 50,000. In other words, they will have a $ 50,000 mortgage. How can you get a mortgage When you find a house you like, you go to a bank. The bank will research your financial (金融的) history and decide if they think you are a good risk. They will want to know what kind of job you have, what kind of salary you make, and how long you have had the job. They will also want to know how much money you have. In addition, the banks will require a down payment. Depending on which state you live in, the bank may require as much as 30% of the price of the house as a down payment. The bank will then lend you the rest of the money to buy the house. Many people are never able to buy a house because they cannot save enough money for the down payment. What does "down payment" refer to in the passage

A. Money borrowed from a bank as a mortgage.
B. Money paid to a bank before the mortgages is given.
C. Interest received by a person who borrows money as the mortgages.
D. Interest charged by a bank on a mortgage.