Officer Castro Notices a Car in Front of Him Driving

Officer Castro notices a car in front of him driving at a slow speed.  The driver seems to be driving erratically. Officer Castro activates his blue lights and attempts to pull the car over.  The driver continues to drive for approximately two additional miles before pulling over.  When Officer Castro slowly approaches the car, he smells what seems to be a heavy odor of marijuana.  The driver has dilated eyes and slurred speech.  There are four individuals in the car.
Officer Castro would like to look in side the car .  He could legally enter the car without a warrant by

A) clai ming non exigent circumstances
B) calling for backup as he examines the ins ide of the car.
C) demanding the driver to let him in.
D) wanting to see the vehicle registration number.