Explanation/Reference:
Explanation:
The security department would be busy in the development phase as it includes the follow security related activities:
Security functional requirements analysis

Identifies the protection levels that must be provided by the system to meet all regulatory, legal, and policy compliance needs.
Security assurance requirements analysis

Identifies the assurance levels the system must provide. The activities that need to be carried out to ensure the desired level of confidence in the system are determined, which are usually specific types of tests and evaluations.
Security plan

Documented security controls the system must contain to ensure compliance with the company's security needs.
Security test and evaluation plan

Outlines how security controls should be evaluated before the system is approved and deployed.
Incorrect Answers:
A: It would be too late to involve the security department during the implementation phase.
B: It would be too late to involve the security department during Testing Phases including the System Testing phase.
C: It would be too late to involve the security department during the Unit Testing phase.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, p. 1091