An entity$-$relationship diagram

a$.$ cannot show multiple relationships between the same two entity types.

b$.$ cannot express a $m$:$n$ cardinality ratio between two entity types.

c$.$ should not have attributes for a relationship type.

d$.$ should show only one unique identifier for each base $($strong$)$ entity type in the model.

e$.$ none of the statements are correct about an entity$-$relationship diagram.