reduce (by) half.

问题描述:

reduce (by) half.
Taking out these smoking scenes could reduce the number of teen smokers (by) half.
为什么不能用to

by half意思是“一半”,而且一般指“减少一半”,本句话的意思就是“把那些吸烟(有害健康)的场景摆出来能让青少年吸烟人数减少一半”.
没有to half用法