The boy is very thirsty. He ______ some water. [ ]

A. is needing

B. do need

C. needs 

D. need

验算某支承工作平台轴心受压缀条柱的整体稳定性。

已知钢材为Q235。柱高4m，l_0x=4m，l_0y=2m两端铰接，轴心压力设计值为2800kN。型钢选用2[40a，面积A=150cm²,i_x=15.3cm³，缀条选用2L45×4角钢，面积A₁=6.98cm²，I_y=64222cm⁴。