buttocks,buttock line是什么意思

用法例句

Under these new conditions, new fluvial trends haveshown on the plain morphology、longitudinal section and cross section in thelower Yellow River.

新的水沙条件和河道边界条件下黄河下游河道平面河势,纵剖面和横断面特征都出现了一些新的演变趋势。