18. GWD17-Q18:
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.

答案是A,   我选的B ， 说不清为什么选B，就是感觉，  可是A我认为有严重错误啊， and 前后一个是句子一个是短语，不能构成平行啊。。。 请高人指点一下！

是啊，不过B的idiom好像有问题啊，最后的in additon to ....有点wordy啊，直接and 不就完了吗

是啊，如果B里把in addition to换成 and,我肯定就一眼选定这个啦。  头痛GMAT里的句子总给人感觉别别扭扭的。

A 确实不对。B 也太累赘。其实 C 最好，只要删去那个 's。

C? 第一眼看到with charcoal's being 就排除了。。。   那这样看来还是B相对最好咯。

B 并不好。最好是这样的：
With charcoal 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.