The 'guess who pop up ding dong' in the teaser was related to Cardi B's lyrics
Does that mean there will be promotional phases for each unit of girls revealed? First a teaser with song lyrics, then promo pics and a cover? 
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The choreo for the recent cover also appeared here. So the order seems to go Dance, Rap, Idol Performance, Dance, and Vocals.
So in the next few weeks, we might be getting promo like this for the rest of the units
