Nice work on this one, everyone. Just figured I'd chime in because the title of this post spoke to me right away:
Researchers at Cornell University have demonstrated that...
As soon as I saw that subject I knew that this problem would be a terrific candidate for what I call the Slash-and-Burn technique to reduce the number of words that you have to read in a sentence.
That first part, ending in the word "that" sets up a new clause..."homing pigeons" after the word "that" becomes the new subject, so you don't need to even bother with the "Researchers have demonstrated that..." portion. Once you know that the new subject that follows is capable of standing on its own, you can break that first part off to read less.
This one also involves a list, and list-based sentences generally need to have parallel form. The easiest place to spot a lack of parallelism is on the verb, because verbs can take a variety of tenses and forms. Seeing that, I'd strip off the object of each verb so that I can just test the verbs themselves. The sentence that I'd end up reading is:
Pigeons can sense X, see Y, detect Z, sense A, and can identify B.
Clearly that extra "can" is redundant and unnecessary and breaks parallelism...the entire sentence is about what pigeons "can" do, so that initial "can" applies to all verbs. That eliminates A and B, and C looks pretty good. D and E each change the verb tense/form:
Pigeons can sense X, see Y, detect Z, sense A, air pressure changes can be/are sensed...
Those sentences break parallelism and in doing so end up as sentence fragments..."changes" as a noun isn't set off as a subject of a new verb by an appropriate transition, so it simply cannot be correct.
Learn to shorten sentences by eliminating irrelevant clauses, descriptive phrases, adjectives/adverbs, etc. and the errors will tend to jump off the screen for you.
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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