The online retailer Ecatalog.com has decided to send consumers of the new John Grisham book an e$-$mail with suggestions for books with similar themes and has also offered them a $20\%$ discount if those suggested books were purchased. This type of marketing$/$promotion is an example of:

a$.$

Cross$-$selling

b$.$

Segmented selling

c$.$

Target marketing

d$.$

Clickstream selling