Hello Everyone!
Let's tackle this question, one issue at a time, and narrow it down to the right choice quickly! First, let's take a look at the original question and highlight any major differences in orange:
As sources of electrical power, windmills now account for only about 2,500 megawatts nationwide, but production is almost expected to double by the end of the year, which would provide enough electricity for 1.3 million households.
(A) almost expected to double by the end of the year, which would provide
(B) almost expected that it will double by the end of the year, thus providing
(C) expected that it will almost double by the end of the year to provide
(D) expected almost to double by the end of the year and thus to provide
(E) expected almost to double by the end of the year, which would thus be providing
After a quick glance over the options, a couple key differences jump out that we can focus on:
1. almost expected vs. expected almost (Adverbs & Meaning)
2. which would provide / thus providing / to provide / and thus to provide / which would thus be providing (Modifiers)
Let's start with #1 on our list because it will eliminate 2-3 options rather quickly. What we're dealing with here is adverb placement. We need to figure out what the adverb "almost" SHOULD be paired up with to determine which one we need:
almost expected to double = refers to the likelihood that production will double at all
expected almost to double = refers to the amount by which production will change
It makes more sense to say that the amount of production might double, and not that production might be expected. So let's rule out any options that don't clearly place the adverb "almost" with "double/s":
(A) almost expected to double by the end of the year, which would provide
(B) almost expected that it will double by the end of the year, thus providing
(C) expected that it will almost double by the end of the year to provide
(D) expected almost to double by the end of the year and thus to provide
(E) expected almost to double by the end of the year, which would thus be providing
We can eliminate options A & B because they don't have the adverb "almost" in the proper place to convey the meaning we're after. Now that we have things narrowed down, let's take a closer look at each remaining option with the non-underlined parts plugged in and determine which is the best one:
(C) As sources of electrical power, windmills now account for only about 2,500 megawatts nationwide, but production is expected that it will almost double by the end of the year to provide enough electricity for 1.3 million households.
This option is INCORRECT because it contains a vague pronoun! It's not clear at all what the pronoun "it" is referring to here - windmills, production, megawatts? If we read this sentence through, the phrase "production is expected that it will almost double" sounds incredibly clunky and awkward as well.
(D) As sources of electrical power, windmills now account for only about 2,500 megawatts nationwide, but production is expected almost to double by the end of the year and thus to provide enough electricity for 1.3 million households.
This is CORRECT! The adverb "almost" is in the right place, there are no issues with parallelism (to double/to provide), and there are no modifier issues.
(E) As sources of electrical power, windmills now account for only about 2,500 megawatts nationwide, but production is expected almost to double by the end of the year, which would thus be providing enough electricity for 1.3 million households.
This option is INCORRECT for a couple reasons. First, it has a ", which"modifier that's being used incorrectly. "Which" modifiers are NOUN modifiers, and they can only modify the noun closest to them. In this case, the modifier is trying to modify the noun "year," which isn't right. The modifier should refer back to "production." It's also incorrect because the two things that production accomplishes aren't written using parallel format (to double / be providing).
There you have it - option D is the correct choice! By focusing on the obvious differences between the options, we can easily weed out wrong choices to get to the right one quickly!
Don't study for the GMAT. Train for it.
