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Sentence Correction: Subject Verb Agreement Questions - Overview

As even most smokers will admit, smoking is both unhealthy and cost a lot of money

This answer choice is grammatically incorrect. The singular subject Smoking does not agree with the plural verb cost.

Remember that a subject in the form of Verb+ing is considered a singular subject.

[[snippet]]

While this answer choice corrects the original Subject Verb Agreement mistake by changing the plural verb cost to the singular form costs, it is still grammatically incorrect . The singular subject Smoking does not agree with the plural verb are.

Did you notice this change from is to are?

This answer choice repeats the original mistake. The singular subject Smoking does not agree with the plural verb cost.

Remember that a subject in the form of Verb+ing is considered a singular subject.

[[snippet]]

Furthermore, this answer choice creates another Subject Verb Agreement mistake by replacing the singular verb is with the plural form are.  

The lesson to be learned here is that you should not automatically choose the first answer choice that corrects the original mistake. After eliminating all answer choices that repeat the original mistake, you have to go over the remaining answer choices and compare them carefully. 

Do not assume that the only thing that changes in the answer choices is the part which was originally flawed. By doing so you risk choosing the wrong answer.

Remember that a subject in the form of Verb+ing is considered a singular subject.

While this answer choice corrects the original Subject Verb Agreement mistake and is grammatically correct, it is not the best of the answer choices. There is another answer choice that is also grammatically correct and is stylistically superior to this one.   

Did you read all the answer choices (the first one doesn't count as it always repeats the original)? 

Very good! This answer choice both corrects the original Subject Verb Agreement mistake and is more concise than the other answer choices, as a result of replacing the five-word phrase costs a lot of money with the single word costly, which means the same.   

That is most probably why you got this question wrong. In Sentence Correction, you do not choose a correct answer choice. You eliminate four answer choices and choose the one that's left. In order to do so, you need to go over all five answer choices.  

After eliminating the answer choices that repeat the original mistake, you need to go over all the remaining answer choices and compare them, eliminating all but one. 

Did you eliminate the last answer choice because you thought it changed the original meaning? 

That is most probably why you got this question wrong. You interpreted a change in wording (cost a lot of money --> costly) as a meaning change. In fact, this change retains the original meaning. 

There should always be a good reason for eliminating an answer choice. Make sure you are aware of why you have eliminated an answer choice. If you don't have a reason, consider that in fact that answer choice might be correct.

is both unhealthy and cost a lot of money
are both unhealthy and costs a lot of money
are both unhealthy and cost a lot of money
is both unhealthy and costs a lot of money
is both unhealthy and costly
Yes
No
Yes
No
Yes
No