为什么千斤顶起重后停留时间较长时应加保险箍？
参考答案：
千斤顶起重后停留时间较长时，在活塞伸出部分安装保险箍可防止重物突然下降而造成事故。
As soon as she entered the room, the girl caught sight of the flowers _________ by her mother.
A．buying
B．being bought
C．were bought
D．bought
防己与防风共有的功效是（）
A.祛风湿
B.止痹痛
C.补肝肾，强筋骨
D.利水消肿
E.清热
