The correct answer is: A. unsolicited e-mail.
Spam is a type of electronic junk mail or junk newsgroup posting. It is an unsolicited message sent to a large number of recipients for the purpose of advertising, phishing, spreading malware, etc. Spam is often sent from compromised computers, and it can be very difficult to stop.
Option B, application, is incorrect because spam is not an application. An application is a computer program that performs a specific task. Spam is not a program; it is a type of message.
Option C, operating system, is incorrect because spam is not an operating system. An operating system is a software program that manages the hardware and software resources of a computer. Spam is not a program; it is a type of message.
Option D, newsgroup, is incorrect because spam is not a newsgroup. A newsgroup is an online discussion forum where people can post messages about a particular topic. Spam is not a forum; it is a type of message.