下面不属于水垢清除方法的是（）。
A、蒸汽吹垢
B、人工除垢
C、机械除垢
D、化学除垢
参考答案：A
While reading, Helen has a habit of stopping _____ to give her long and flowing hair a smooth.
A．occasionally
B．eventually
C．automatically
D．absolutely
《建筑机械与设备分类》共划分为（）大类。
