Which of the following can be used to sign stored procedures?

CORRECT TEXT
You work as a senior developer at ABC.com. The ABC.com network consists of a single domain
named ABC.com.
You are running a training exercise for junior developers. You are currently discussing the process
of signing stored procedures in SQL Server 2012.
Which of the following can be used to sign stored procedures? (Choose two.)

A.
An asymmetric key.

B.
A master key.

C.
A symmetric key.

D.
A certificate.