题目

阅读理解 The burst of barking suddenly woke me up. It was 2:30 a.m. in the early morning. Wondering why Rock was making so loud noises, I decided to go to him. By the time I made it to the bottom of the stairs, he was running up. I felt strange, for he had never come up the stairs, no matter what. I think that was his way of telling me, “We've got to go back up.” When I got to the top of the stairs, I turned around and saw a light on, but I didn't remember leaving one on. I walked downstairs again, and that's when I saw fire. I immediately shouted to my wife to wake up and get our thre已知函数的最大值为，最小值为，若向量与向量垂直，则锐角的值为（    ）A．B．C．D．