What are two reasons an existing custom field cannot be marked as External ID? Choose 2 answers


What are two reasons an existing custom field cannot be marked as External ID? Choose 2 answers
A . Maximum number of External IDs allowed on an object has been reached,
B . Maximum number of fields of an object has been reached.
C . Maximum number of skinny tables has been reached.
D . Maximum number of indexes allowed on an object has been reached.

Answer: A,D