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Sentence Correction: Parallelism Questions - Overview

Washing dishes by hand uses a much larger amount of water as using a machine although machines use electricity, require maintenance, and take up space.

This answer choice is illogical and grammatically incorrect. The word larger (or any adjective+er) cannot be complemented by as because larger indicates an inequality between the two things compared whereas as indicates a similarity between them. 

What helps us identify this question as a Comparative question as well as identify the mistake is the following Stop Sign:

Like, unlike, than, as

Great work!

This answer choice corrects the original Comparative error by replacing as with than and adds a conjugated verb in the second part of the comparison, as preferred in the GMAT.

Although this answer choice corrects the original Comparative error by replacing as with than, it is not the most stylistically sound. A stylistic preference in Comparative questions is that there should be a conjugated verb in the second part of the Comparative construction (i.e., after the word than). 

There is an answer choice that is both grammatically correct and includes a conjugated verb in the second part of the comparison. Look for it!

Although this answer choice corrects the original Comparative error by replacing as with than, it is grammatically incorrect. The first two items in the list at the end of the sentence are verbs (use, require), but the last item is a noun (spaces).

What helps us identify this question as a Parallelism question as well as identify the mistake is the following Stop Sign:

A list of 3 items or more, separated by commas and and/or before the last item.

Although this answer choice corrects the original Comparative error by replacing as with than, it is grammatically incorrect. The first and last items in the list at the end of the sentence are verbs (require, take), but the middle item is an adjective (electrical).

What helps us identify this question as a Parallelism question as well as identify the mistake is the following Stop Sign:

A list of 3 items or more, separated by commas and and/or before the last item.

as using a machine although machines use electricity, require maintenance, and take up space
than using a machine does although machines use electricity, require maintenance, and take up space
than using a machine although machines use electricity, require maintenance, and take up space
than using a machine does although machines use electricity, require maintenance, and large spaces
than using a machine does although machines require maintenance, electrical, and take up space