标题: prep 160, 关于it的指代问题 [打印本页] 作者: boboowu 时间: 2010-12-10 12:54 标题: prep 160, 关于it的指代问题 In a previous design, the weight of the discus used in track competition is concentrated in a metal center, but now it is lines with lead around the perimeter, thereby improving stability in flight and resulting in longer throws.