题目

Do you want to improve the way you study? Do you feel nervous before a test? Many students say that a lack of concentration is their biggest problem.     16     If so, use these tips to help you. Study Techniques 17    You shouldn’t sit somewhere that you use for another purpose. For example, you always study at the desk, but when you sit on a sofa to study, your brain will think it is time to relax. Before sitting down to study, bring together all the equipment you need.    18   If your study desk or table is needed when you are not studying, store all your equip如图，正方体的棱长为1，线段上有两个动点，且；则下列结论错误的是（ ）A. B. 平面C. 三棱锥的体积为定值 D. 的面积与的面积相等