d af lc center ~4∽;+s/vele rt. mer tal e 三i9 ane o r J 22r +e~(+ R;-以he × Assume:Ear*iw,r+,m为a Nke水R 已 f ne s, 0:^5ky 已ce Ss 0 S/c X aⅵ He plame of fhe tract