题目

.He has got himself into a dangerous situation ____ he is likely to lose control over the plane.        A.where     B.which     C.whileD.why 答案：A我们知道声是由振动的物体发出的．但有时候，比如敲桌子时，我们能听到声音，却看不见桌子的振动，请你设计实验证明桌子在振动．写出实验器材、实验过程、实验现象、实验结论．