请教几道题

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.

The answer key  is  A, but   I feel C is better..?

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According to a survey of graduating medical students
conducted by the Association of American Medical Colleges, minority graduates
are nearly four times more likely than are other graduates in planning to
practice in socioeconomically deprived areas.

1. minority
        graduates are nearly four times more likely than are other graduates in
        planning to practice
2. minority
        graduates are nearly four times more likely than other graduates who plan
        on practicing
3. minority
        graduates are nearly four times as likely as other graduates to plan on
        practicing
4. it is
        nearly four times more likely that minority graduates rather than other
        graduates will plan to practice
5. it is
        nearly four times as likely for minority graduates than other graduates to
        plan to practice

For protection from the summer sun, the Mojave lived in
open-sided, flat-topped dwellings known as shades, each a roof of poles and
arrowweed supported by posts set in a rectangle.

1. each a
        roof of poles and arrowweed
2. each a
        roof of poles and arrowweed that are being
3. with
        each being a roof of poles and arrowweed
4. with
        roofs of poles and arrowweed to be
5. with roofs of poles and
   arrowweed that are

1). think about these: being is often wrong...; 主动〉被动；

2). plan to do; as ...as 连用， more...than连用；than后面谓语动词的尽量补出原则；

3）each a roof...in a rectangle..是同谓语，解释shades,所以不能用with连词(这个是不是有限制的意思啊？），(不确定解释的对不对*0*）后面的that are 也是多余的