题干

若函数fx=x2+ax+b有两个零点cosα,cosβ,其中α,β0,π,那么在f-1,f1两个函数值中  (    )

A:只有一个小于1

B:至少有一个小于1

C:都小于1

D:可能都大于1

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答案(点此获取答案解析)

B

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    As I walked along the Edgware Road, I felt as though the world was closing in on me. All the sounds I take for granted, had gone. I had entered a world of silence. This unsettling experience occurred a few weeks ago when I agreed to go deaf for the day to support the work of the charity Hearing Dogs for Deaf People, for which I am an ambassador.

    When I managed to take a cab to the office of my manager, Gavin, I couldn't hear what the taxi driver was saying to me. Conversation was impossible. Then, when I reached the office, I had to ring the intercom five times as I couldn't hear a response.

    Everybody said I was shouting at them—I simply wasn't aware of how loudly I was speaking as I couldn't hear my own voice. Gavin kept telling me my phone was ringing, but I didn't realize. I was too busy trying to concentrate on reading his lips. And when he tried to tell me a code to put into my phone, I had to keep asking him to repeat it, more slowly. Eventually he lost his patience and snapped at me: “Just give me the phone!” I was shocked.

    People couldn't be bothered to repeat themselves, so they kept trying to do things for me that I was perfectly capable of doing myself. I felt I'd lost control.

    Being deaf for the day was extraordinarily tiring. I had to work so hard to “listen” with my eyes, get people's attention and use my other senses to make up for my lack of hearing. It was a huge, exhausting effort.

    Until that experience I didn't realize how much I took my own hearing for granted, or the sorts of emotions and experiences deaf people go through. If a deaf person asks you to repeat something, never think: “It doesn't matter.” It does matter.