A7,B7,C7,D7 Chord Practice

In this video i tried to learn dominant 7th chords, i posted this video in order to complete week1 blog reflection video task. In this video i played A7,B7,C7,and D7 chords. Actually this kind of chords is familiar with me, but i never realize the name of the chords. I hope i can improve and learned deeper about the things that i played