The Cisco IDM Custom Signature Wizard asks you to select between the protocol types IP, ICMP, UDP, and TCP under which circumstance?

A.
when you specify the String engine

B.
when you specify the Service engine

C.
when you specify the Atomic engine

D.
when you specify the String or Service engine

E.
when you do not select a specific engine

Explanation:
http://www.cisco.com/en/US/docs/security/ips/7.0/configuration/guide/idm/idm_signature_wizar d.html#wp1655660