Which of the following is NOT a characteristic of a unique index?

A.
Each column in a base table can only participate in one uniqueindex, regardless of how the
columns are grouped (the same column cannot be used in multiple unique indexes)

B.
In order for an index to be used to support a unique constraint, it must have been defined with
the UNIQUE attribute

C.
A unique index cannot be created for a populated table if the key column specified contains
more than one NULL value

D.
A unique index can only be created for a non-nullable column