Her father was a quiet man with ____(grace) manners.
显微镜下观察小鱼尾鳍的毛细血管时,应该寻找( )。
如图是一个横断面为抛物线形状的拱桥,当水面宽4m时,拱顶(拱桥洞的最高点)离水面2m,当水面下降1m时,水面的宽度为( )