Which of the statements below is$/$are correct? $($More than one selection possible.$)$

A$.$

Reducing number of attributes in a dataset is a data transformation subtask.

B$.$

For numerical variables, standardizing the observed values so that they lie between $0$ and $1$ is a data transformation subtask.

C$.$

Converting numerical variables into discrete representations is a data reduction subtask.

D$.$

Accessing and collecting relevant data after deciding which sources to use is a data consolidation subtask.