Officer Goldman Responds to a Call of an Active Shooter

Multiple Choice

Officer Goldman responds to a call of an active shooter during a home invasion at a local residence.  Officer Goldman arrives on the scene and quickly surveys the residence.  He and his partner immediately enter the home and see the suspect.  They command the suspect to drop his weapon, and the suspect responds by dropping the weapon.  Officer Goldman arrests the suspect and searches him.
Once the suspect is taken into custody, Officer Goldman immediately searches him.  He is allowed to do this without a warrant due to:

A) search incident to a lawful arrest.
B) consent.
C) exigent circumstances.
D) the  exclusionary rule.