After the departure of a developer under unpleasant circumstances, the company is concerned about the security of the software to which the developer has access. Which of the following is the BEST way to ensure security of the code following the incident? 

Answer options:

A. Hire an external red team to conduct black box testing
B. Conduct a peer review and cross reference the SRTM
C. Perform white-box testing on all impacted finished products
D. Perform regression testing and search for suspicious code

A