题目

硅元素在自然界的主要存在形式是 A．晶体硅    B．二氧化硅      C．硅酸        D．硅酸盐 答案：D-The weekends are coming .Let's go to fly kites in the park.- A. How exciting! B. You are welcome.C. Have a good time! D. Not at all.