经济流速法确定管径适用于有泵管路系统中管径的计算。
参考答案：对
A mixture of joy and anxiety ______ me as I watched the rocket soaring upward into the deep
universe. [ ]
A. held
B. caught
C. settled
D. measured
从物理特性看，（）非常坚硬，从而增强了细胞壁的硬度。
A.纤维素
B.木质素
C.果胶质
D.胼胝质
