A Denial of Service (DoS) attack is:（）

• A、an attempt to bring down a website or other online service.
• B、a prank where someone sends an unauthorized e-mail attempting to close a user’s e-mail account.
• C、stealing a user’s identity and making changes to their accounts.
• D、an attempt to change a user’s password to prevent access to a service by repeatedly guessing the user’s information.