Replication Controller monitors Replica Sets?

Course Name: CKA
In the video at the timestamp 1:50 the instructor said RC continuously monitors the status of RS.
RC and RS both are different types of controllers type then how come RC can monitor the RS?

URL: CKA Certification Course – Certified Kubernetes Administrator | KodeKloud

Note: RC - Replication Controller
RS - Replica Set

Can someone please reply