建筑外门窗抗风压性等级3.0≤P3<3.5属于（）级的指标值。
参考答案：五
It was from John, ____ gave me a big key to _____ my dad.
A．who; understand
B．that; understanding
C．who; understanding
D．which; to understand
对于单个刚体，通过空间汇交力系的平衡方程最多可求得（）个未知量。
A.2
B.3
C.4
D.6
