A . True. The GROUP BY clause needs to include all non-aggregated columns from the SELECT list to provide the correct grouping for the output. The output shown in the image indicates that the data is grouped by channel_type, month, and country_code.
B, C, and D are incorrect because:
B includes a ROLLUP which would introduce subtotals that are not reflected in the output shown.
C specifies a CUBE, which would produce all possible combinations of groupings including the grand total, which is not shown in the output.
D specifies a ROLLUP on country_code only, which would not correctly group by channel_type and month.