When is the GROUP BY ROLLUP clause used in an OLAP query?

When is the GROUP BY ROLLUP clause used in an OLAP query?
A . All subtotals and grand totals are to be included in the output
B . Subtotals are only to be included in the output
C . Grand totals are only to be included in the output
D . Specific subtotals and grand totals for a combination of variables are only to be included in the output

Answer: A