What do you have to consider when you create a query with multiple structures?

What do you have to consider when you create a query with multiple structures?
A . By using both the structures in the rows or in the columns you can avoid formula collision.
B . You must use one structure in the report columns and one structure the report rows.
C . You must use a maximum of two structures.
D . You can only use one structure with key figures in a query.
E . You can only use one structure without key figures in a query.

Answer: C,D