To avoid being intrusive and annoying, most legitimate email marketers practice which means sending email pitches only to customers who "opt in."

To avoid being intrusive, and annoying, most legitimate email marketers practice, email marketing, which means sending email pitches only to customers who, "opt in."

Email marketing is the practicing of promoting a product or service through the internet using email addresses of potential customers that previously registered in your mailing list and hence are willing to receive information about your products or services.

answer(b); ; ; the quantitative or qualitative variable for which the experimenter wishes to determine how its value is affected by the explanatory variable;