题目

The human body is a machine that can raise lots of interesting questions. Why, for example, are yawns（呵欠）contagious（传染的）? What's up with ice-cream headaches? Here are answers to these and other questions about our bodies.Why do I get a headache when I eat ice cream too quickly?Scientists aren't exactly sure what causes the brain freeze when we eat ice cream or other super cold foods too quickly, though some believe it's the result of changed blood .flow in the nervous system. Blood vessels in the head tighten to stop the loss of body heat and then relax to let blood flow rise对于任意实数x，不等式（a-2）x2-2（a-2）x-4＜0恒成立，则实数a取值范围（　　）A．（-∞，2）B．（-∞，2]C．（-2，2）D．（-2，2]