All-time first week album sales chart for k-pop girl groups

So, here's the all-time first week album sales chart for k-pop girl groups(so far). As you can see below, it is very notable that TWICE is very strong on the chart even through it has been only 2 years since the girl group debuted, while Girls' Generation, who's maintaining its position as the most popular and influential k-pop girl group is taking 13 of 20 spots of the top 20 of the chart.

<K-pop Secret Vol.2: Unknown Stories about K-pop Industry>
K-pop Secret Vol.2 contains unknown stories about k-pop industry. The author, who has been working as a k-pop journalist since 2010 gives you answers to some questions about k-pop industry such as “Do k-pop idols really sing live?” “How do k-pop chart shows choose their no.1 of the week?” and “Who’s the best singer among k-pop idols?”