Rookie group Bay.B, who is currently promoting with "Quecera Cera", released a practice video from before their debut, once again wowing the crowd!

They covered another talented group by singing Big Mama's "Betrayal" and "Never Mind", showing off their own powerful and mature vocals -- not to mention, impressive harmonization and diverse range.

SEE ALSO: Bang Ye Dam apologizes to fans for the video filmed in his studio by his friend Lee Seo Han

Check out the video above and prepare to be blown away!