Collaborative filtering is

a. used by ISP's to filter out email SPAM
b. based on information about one’s preference and that of others.
c. a way to help an individual focus on best choices when deciding what to watch or buy.
d. used by online retailers and movie streaming sites to censor information

A: used by ISP's to filter out email SPAM

C: a way to help an individual focus on best choices when deciding what to watch or buy.

Explanation:

Collaborative filtering uses a community-based approach to filter spam. It works by collecting numerous email users from around the world. By doing this, it becomes possible for users to flag emails that are spam and those that are legitimate.

Also Collaborative Filtering is one of the most efficient techniques for building a system that can help a user when it comes to recommending best choices based on information from a large number of users.

answer; i believe the correct answer is (expression); good luck

i prefer xbox one. : )