What do you wear to ________?[ ]
A. swim
B. swimming
C. swims
D. swam
答案:A
试用杂化轨道理论分析为什么BF3的空间构型是平面三角形,而NF3是三角锥形的?_____________________________________________________________________________________________________
轻型滑轮装置极限负荷不小于22kN。