I suggested to my mother that she_______a drawing club after her retirement form teaching.

A．join

B．joins

C．joined

D．would join

某自重湿陷性黄土场地混凝土灌注桩桩径为800mm，桩长为34m，通过浸水载荷试验和应力测试得到桩身轴力在极限荷载下（2800kN）的数据及曲线图如下，试计算桩侧平均负摩阻力值。