Practices by a certain group of people is known as? a. customs b. beliefs c. traditions d. norms

Practices by a certain group of people is known as : A. Customs

For example, it is a custom in Japan to bow down when you introduced yourself to someone at the first time. 

Custom tend to be only applied to a specific group of people. If a member of that group of people failed to follow the custom, he/she tend to received social punishment such as social exclusion

hope this helps

A custom (also called a tradition) is a law or right or usual way, which is not written and is in practice since a long time. It is any thing which lots of people do, and have done for a long time. Usually, the people come from the same country, culture, time or religion.so a is right option