What caused the fall of the Zhou dynasty

The primary cause for the collapse of the Zhou dynasty was the implementation of the fengjian system, where the royal family would strengthen their authority over the other states by installing relatives as lords in the regions.

The Zhou system was unstable, having to deal with chronic warfare between the various substrates and outsiders. Over the centuries, larger substates conquered smaller ones. The worst warfare occurred during the Era of the Warring States, beginning around 500 C.E. Local dukes ignored the Zhou king and fought among themselves for supremacy. The last of the Zhou states were eventually conquered by the Qin in 221 C.E.

i believe your answer is d)