The delegate promised to continue efforts to reduce by half the number of hungry people by 2050
问题描述：
The delegate promised to continue efforts to reduce by half the number of hungry people by 2050
并且解释一下句中第一个by怎么解释
答
代表团成员承诺（他们）会继续努力,在2050年之前让遭受饥荒的人数减少一半.
第一个BY的用法就是后面加上一个表示数字的词