题目

DOGS DRIVE CAR Auckland, New Zealand     After two months of learning, Monty, and Porter were able to drive an automobile around a racetrack. “We wanted to prove how smart rescue dogs are,” animal behaviorist Mark Vette says. Vette first used voice commands and treats to teach the dogs how to turn a steering wheel and how to change gear(换挡).     The dogs’ ride only accelerated up to 7.5 miles an hour, and trainers could stop the auto using a remote control. GOLDEN ZEBRA Kailua-Kona, Hawaii     Zoe the zebra’s markings are special. The animal has white and golden str已知|OA|=1，|OB|=3，∠AOB=5π6，点C在∠AOB外且OB•OC=0．设实数m，n满足OC=mOA+nOB，则mn等于（　　）A．-2B．2C．3D．-3