There are hopeful signs that we are shifting away from our heavy reliance on fossil fuels: more than ten times as much energy is generated through wind power now than it was in 1990.
A.) generated through wind power now than it was
Wrong use of the idiom "as much as".
B). generated through wind power now as it was
Wrong, because the "as" is followed by a subject pronoun "it". Putting a noun after "as" is confusing by suggesting functional comparison or by turning the "as" into the subordinating conjuntor; here with the possible meaning of "because". For more about that aspect of using "as" see: Manhattan SC, p. 144.
C). generated through wind power now as was the case
Correct, because the verb "was" after the "as" eliminates the confusion described under B). Correct idiom form is used too. One may suspect wordiness here, but the sentence is very clear, isn't it? I seldom go for patterns in 700+ problems.
D). now generated through wind power as it was
Wrong for the same reason as B).
E). now generated through wind power than was the case.
Incorrect use of the idiom "as much as".
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