Which stored procedure option should you use?

You are a database developer at an independent software vendor. You create stored
procedures that contain proprietary code.
You need to protect the code from being viewed by your customers.
Which stored procedure option should you use?

A.
ENCRYPTBYKEY

B.
ENCRYPTION

C.
ENCRYPTBYPASSPHRASE

D.
ENCRYPTBYCERT

Explanation:
Reference:
http://technet.microsoft.com/en-us/library/bb510663.aspx
Reference:
http://technet.microsoft.com/en-us/library/ms174361.aspx
Reference:
http://msdn.microsoft.com/en-us/library/ms187926.aspx
Reference:

http://technet.microsoft.com/en-us/library/ms190357.aspx
Reference:
http://technet.microsoft.com/en-us/library/ms188061.aspx