阅读下列短文，从每小题的三个选项中选出最佳选项。

    Hello, I'm Ann. This is my family. There are five people in my family. My grandparents are old. They are teachers. My father is tall. He has a white shirt. He is a fireman. He is not afraid of fire. He can help people. He likes his job. My mother is tall and beautiful. She has long hair. She has a yellow skirt. She is a nurse. I don't have any aunts. What about you?

写出下列概念的象征义：

①灰色的幔：____。

②苍蝇、蚊子和蝉儿：____。

③大雷雨：____。

证明：当x∈0，1时，$\frac{\sqrt{2}}{2}$x≤sinx≤x．