Which of the following options are recommended when it comes to uniquely identifying contacts?

You want to update your contact database .

Which of the following options are recommended when it comes to uniquely identifying contacts? Note: There are 3 correct Answer to this question.
A . Use date of birth.
B. Use email address.
C. Use first name and last name.
D. Use an external ID.
E. Use an SAP Emarsys Customer Engagement internal ID.

Answer: B,D,E