What were the effect of zhou metal workers mastering iron? select all that apply

The effects of Zhou metal workers mastering iron were…

Option A: during the  Zhou dynasty, China was characterized by warfare, political and military reforms, but it was first unified during the Qin dynasty.

Option B: it is true that with the introduction of iron, China acquired stronger and more effective farm tools as well as increasing crop yield.

Option C: during the Zhou dynasty China not only developed iron technology but also improved technology of war making better weapons by means of smelted iron. As a result, iron weapons spread to the masses, contributing to the Warring States period.

Option D: it is also true that the Zhou jealously guarded the secret of smelting the iron and created a trading empire. The iron production encouraged trade and improved the empire economy.

Option E: Zhou craftsman are known for their iron art and it is still sold today. During the Zhou period, the craftsmanship had great importance for his skills for producing sophisticated iron weaponry.  

Option F: Iron helped the Zhou rulers so much that they reserved the Mandate of Heaven for themselves alone. It was a period of cultural and intellectual expansion during Zhou era and the iron helped rulers keep the control of the land .

The correct answers are the following:

Answer B: Iron made stronger, more effective farm tools and increased crop yield.

Bronze was replaced by iron, and thanks to trade, it became more and more important among states within China. Some of the changes in agriculture included the use of the iron plough, which really expanded crop yields, leading to an explosion of population. Moreover, there were some large-scale works like Dujiangyan Irrigation System and the Zhengguo Canal, which also incremented agricultural production.

Answer C: Iron weapons spread to the masses, contributing to the Warring States period.

With the population explosion, the number of commoners got so high that it got out of the aristocracy's control. And iron technology produced a new generation of weapons, really cheaper and easier to make than the bronze weapons used by previous generations. At the same time that populations grew, wars started to take place between commoners against one another. Eventually, after the Warring States period, battles between huge armies were being fought on eastern China.

d: their own individual powers within the new goverment