题目

After school we went to the reading-room to do some reading, only to be told that it _______ for one week. A . was decorated B . had decorated C . had been being decorated D . was being decorated 答案：C如图，碗中盛有一碗水，一根粗细均匀的木筷静止在如图所示的位置，木筷右上端与碗沿接触点为O点．请你以O点为支点，画出木筷所受重力及浮力的示意图，并标明重力和浮力的力臂．