To perform split$-$apply$-$combine, we can use which of the following?

Select one:

a$.$ 'groupby' for both splitting and combining, 'apply' for applying

b$.$ 'groupby' for splitting, 'apply' for applying and 'aggregate' for combining

c$.$ 'split' for splitting, 'apply' for applying and 'groupby' for combining

d$.$ 'aggregate' to do all three steps