The BSD subsystem in the OS X kernel (XNU) provides the primary system program interface. BSD is a key component responsible for user-level functionalities and system interfaces, making it the correct answer.

The email John received is an example of a chain letter. Chain letters are messages sent over email that urge the recipient to forward the email to a certain number of people. They often promise rewards for doing so or threats for not complying. In this case, the email promises prizes for forwarding it to many people, fitting the description of a chain letter perfectly.
The Electronic Communications Privacy Act of 1986 (ECPA) allows the FBI to issue National Security Letters (NSLs) to Internet service providers (ISPs) ordering them to disclose records about their customers. This act was designed to extend government restrictions on wire taps from telephone calls to include transmissions of electronic data by computer, thus making it applicable to ISPs.
Windows can be easily identified with the help of TCP FIN scanning because unlike most Unix-based systems, Windows does not conform to the standard protocol behavior for handling FIN packets on open ports. When a FIN packet is sent to an open port in Windows, it responds with a RST packet instead of dropping the packet, making it easily identifiable via FIN scanning.