GWD-TN-14 18题 做语法做的要崩溃了

Over the course of the eighteenth
century, the average output of ironwork tripled as a result of several
improvements in blowing machinery and because coal replaced charcoal as the
fuel used in the smelting of iron ore.

A.     
Over the course of the eighteenth century, the average
output of ironwork tripled as a result of several improvements in blowing
machinery and because coal replaced charcoal as the fuel used in the smelting
of iron ore.

B.      
Over the course of the eighteenth century a tripling in the
average output of ironwork was due to the replacement of charcoal by coal for
the fuel used in the smelting of iron ore, in addition to several improvements
in blowing machinery.

C.     
With charcoal’s being replaced by coal as the fuel used in
the smelting of iron ore and several improvements in blowing machinery, the
average output of ironwork tripled over the eighteenth century.

D.     
The replacement of charcoal with coal for the fuel used in
the smelting of iron ore and several improvements in blowing machinery, the
average output of ironwork tripled over the eighteenth century.

E.      
Charcoal being replaced by coal as the fuel used in the
smelting of iron ore, and several improvements in blowing machinery, which
tripled the average output of ironwork over the course of the eighteenth
century.

请教下句子的重心怎么分析，几个选项是否句子重心不同呢？

as a result of 和because有重复的嫌疑吗？中间用and连接那就是要平行对称吧，但是这两个句子之间的关系我不太清楚，也没看出平行对称。

跪求NN解答啊～谢谢