Anti-spam software can prevent unwanted mail by either filtering

Question

Anti-spam software can prevent unwanted mail by either filtering incoming messages with the aid of rule-based filters or  asking users to blacklist the addresses sending them  junk mail.

A. asking users to blacklist the addresses sending them
B. asking users to blacklist the addresses, sending them
C. by asking users to blacklist the addresses from which they are sent
D. ask users to blacklist the addresses sending
E. by asking users to blacklist the addresses that send

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fdfd97 · Answer

"by" is outside the parallelism as it is before "either". This eliminates C and D
D doesn't maintain the parallelism of either filtering.... or asking.... This eliminates D
B implies that "sending them" is outside the parallelism, which distorts the actual implied meaning of the sentence.
So, the correct answer should be Option A.

Archit3110 · Answer

co relative conjunction 
by either X or Y
either -ing .... or -ing llism
only option A & B left
use of , in option B is not required
hence option A is correct

Bunuel · Answer

OFFICIAL EXPLANATION

Anti-spam software can prevent unwanted mail by either filtering incoming messages with the aid of rule-based filters or  asking users to blacklist the addresses sending them  junk mail.

A. asking users to blacklist the addresses sending them

The original sentence correctly uses parallelism with the  either...or  structure:  by either (1) filtering ... or (2) asking ...

Although this answer choice is stylistically flawed because of a pronoun ambiguity ( them  can refer either to  addresses  or  users ), it is the only answer choice that is grammatically correct and retains the original meaning. Therefore, it is the best answer choice.

B. asking users to blacklist the addresses, sending them

Incorrect.

This answer choice changes the original meaning of the sentence. By adding a comma, it separates the phrase  sending them junk mail  from the original  the addresses (that are) sending them junk mail . This new separate phrase implies that the anti-spam software sends junk mail.

C. by asking users to blacklist the addresses from which they are sent

Incorrect.

This answer choice is grammatically incorrect. In the list  by either filtering ... or ... , the part of speech that follows  either  must also follow  or . In this answer choice,  either  is followed by a verb:  filtering. Or , however, is followed by a preposition:  by .

What helps us identify this question as a Parallelism question as well as identify the mistake is the following Stop Sign: (n)either... (n)or...

D. ask users to blacklist the addresses sending

Incorrect.

This answer choice is grammatically incorrect. In the list  by either filtering ... or ... , the part of speech that follows  either  must also follow  or . In this answer choice,  either  is followed by  filtering , a V+ing verb.  Or , however, is followed by  ask , a base formverb.

E. by asking users to blacklist the addresses that send

Incorrect.

This answer choice is grammatically incorrect. In the list  by either filtering ... or ... , the part of speech that follows  either  must also follow  or . In this answer choice,  either  is followed by a verb:  filtering . Or, however, is followed by a preposition:  by .

Anti-spam software can prevent unwanted mail by either filtering

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Anti-spam software can prevent unwanted mail by either filtering

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