.

--- I think this accident happened for many reasons.

--- Richard is partly to blame, __________way you look at it.

A．what

B．which

C．whatever

D．whichever

高度为H的挡土墙，墙背直立、墙后填土面水平。填土是重度为γ、内摩擦角φ=0、粘聚力为c的粘土，墙与土之间的粘聚力为c_a，外摩擦角δ=0。若忽略拉裂的可能性，试证明作用于墙背的主动土压力为：