一般横吹效果比纵吹好，不仅能将电弧吹长，而且气流可穿透弧柱中心，而纵吹是沿着电弧纵向吹动，难于吹到电弧中心。故灭弧性能稍差
参考答案：对
简述教育目的的层次结构。
. While typing, Helen has a habit of stopping _____ to give her long and flowing hair a smooth.
A．occasionally
B．simultaneously
C．eventually
D．directly
