Final answer:
Cassandra is engaging in Email marketing by sending out monthly electronic newsletters to past customers, fitting the profile of Internet and email users who are typically younger and tech-savvy.
Step-by-step explanation:
Cassandra's practice of sending out a monthly electronic newsletter to past customers to advertise her bed-and-breakfast's special events and discounted rates is known as c) Email marketing. This method is part of the digital marketing strategies that leverage the Internet and email to deliver promotional messages to consumers. It is especially effective for reaching a technologically savvy audience that uses the internet regularly, which includes a wide demographic, albeit skewing towards younger, more educated professionals.