Parallelism is an error-type that anyone who has ever prepped for GMAT® Sentence Correction will know. It is a very popular error type with test-takers since it is easy to spot and eliminate incorrect answer options. But there is a specific kind of parallel structure that the GMAT® test-makers disguise so well that it is almost impossible to pick!

The GMAT® question below is the perfect example.

In no other historical sighting did Haley’s Comet cause such a worldwide sensation as did its return in 1910-1911.
(A) did its return in 1910-1911
(B) had its 1910-1911 return
(C) in its return of 1910-1911
(D) its return of 1910-1911 did
(E) its return in 1910-1911

Test-takers usually tend to browse faster through shorter sentences since they are simpler to process. Also, in such sentences as the one above, both the sentence and the underlined part are very small are kept very small, creating an illusion that the question is a rather simple one. But it is far from simple.

Most test-takers would straight away reject (C) and (D) since they “feel” and quickly decide that return of is incorrect. Of the remaining options, they reject (B) since it uses had. Between (A) and (E) it is a toss up, with some test-takers choosing (A) and other (E) since the latter is shorter.

This is actually a perfect example of test-takers barking up the wrong tree.

What the question is actually testing is your understanding of parallel structure. This structure is best revealed upon reading the sentence purely for its structure.

IN no other did X cause such……………… as IN

The as has to be followed by IN, since the sentence starts with an IN.

For example — In no other match did he play as aggressively as in his comeback match of 1975.

The only option that corrects this error is option (C). The GMAT® question below is a very good example that reiterates this particular aspect of parallel structure.

That the new managing editor rose from the publication’s “soft” new sections to a leadership position is more of a landmark in the industry than her being a woman.
(A) her being a woman
(B) being a woman is
(C) her womanhood
(D) that she was a woman
(E) that she is a woman

Upon close observation it can be seen that both sentences are very similar — a very small portion of the sentence is underlined and on the face of it no major error is being tested!

But it is again testing your understanding of parallel structure — THAT she is X is more of a landmark than THAT she is Y.

So than has to be followed by THAT. Only two options correct this error (D) and (E) and the former is wrong because it uses “was”. Most test-takers end up choosing (A) since they can’t seem to find anything wrong with it.

The tougher Sentence Correction questions on the GMAT® test will your understanding of sentence structure. Being able to read for structure will go a long way in helping you go beyond your usual strike-rate in Sentence Correction.

The best way to learn to read for structure — using Xs and Ys — is to read the answer explanations in the Official Guide, that is how I learned to do it.