Unlike many United States cities, where a river is no longer

[RonPurewal]

alternatively, you can notice the same type of problem from a different angle: "but" is nonsense in choice D.
this is something you can notice even if you DON'T figure out the intended meaning.

look at the main structure of choice D:
"[modifier] + a river is the focal point of urban life, BUT the river in San Antonio winds through the middle of the business district and xxxx."
there's no contrast here at all! we have [modifier] + "things are built around rivers" + BUT + "even more things are built around rivers".
you can see that this is nonsense even if you have no idea what the sentence SHOULD say.

[YANFEIG811]

the correct answer here is still pretty ugly, so let's criticize the four incorrect choices.

choice a:
faulty comparison:
'unlike many u.s. cities, ... the river in san antonio...' --> can't compare cities to a river

choice b:
comparison isn't so good:
the second part should start directly with 'the river' (instead of 'in san antonio the river...'), so that the comparison is more clear.
much more importantly, poor use of the relative pronoun 'which':
'...cities in the united states, which is no longer the focal point...'
relative pronouns like which, by default, refer to the noun that's closest to the left, which in this case is the united states. therefore, this relative pronoun is used in a way that's either ambiguous (if you allow it to potentially refer to other nouns) or just plain wrong (if you follow the rule strictly).

choice c:
faulty comparison again
'the river...' is being compared to san antonio.

choice d:
drastic change in meaning
this sentence has completely gotten rid of any reference to the concept of 'no longer'. while all the other sentences say that things have changed, this sentence presents the situation as if it's always been that way.

Hi Ron - I have a question regarding to your explanation for choice D. You said that the main issue for D was that it changes the original meaning of the sentence. However, since there is no background of the 'sentence correction' questions, we do not know what the original meaning is. For this questions, I would say that the meaning in choice D is the correct meaning, and the others are not.

I think this type of questions happens a lot in GMAT SC, but I have been always confused about the explanation of the wrong answer by saying that it changes the original meaning of the sentence.

[RonPurewal]

you can tell that's the intended meaning because of the presence of "today". if this situation has always been the same, then introducing "today" creates nonsense.

[YANFEIG811]

you can tell that's the intended meaning because of the presence of "today". if this situation has always been the same, then introducing "today" creates nonsense.

Thanks, Ron. Let me explain it again to make sure we are on the same page.
I think D wants to say if rivier is still the focal point in US cities TODAY. The conclusion is that no, it is not in many cities, but yes in San Antonio. D does not compare before vs today. Therefore, use 'today' does not make sense. Is that correct?

E wants to compare now vs before. It implies that many cities in US had river as the focal point BEFORE, but not any more in TODAY. While San Antonio still has rivier as the focal point.

Please let me know if I understand it correctly.

In addition, except for the meaning issue, does D have the grammar issue?

The last confirmation want to get from you is that the the meaning in choice A/the original sentence is not necessary correct, right?

Really appreciate your help!

[RonPurewal]

your understanding of the meaning difference is accurate.

there are no significant grammatical issues with choice D.

[RenanP913]

Ron, quick question:

(1 ) Is it an issue to have a modifier in between the "Unlike X, Y" Structure (Unlike X, MODIFIER, Y)? Is there a need for "Y" to always be right next to "X"?

(Seen in A - ignore the parallelism issue) Unlike many United States cities, where a river is no longer the focal point of urban life, the river in San Antonio

(2) Depending on your answer above, had the sentence been structured differently (see below), would it have been correct to say:

(Slight restructuring of answer choice B) Unlike the river in many cities in the United Stated, which is no longer the local point of urban life, the river in San Antonio ...blah blah (pretend that the meaning still works). Unlike the river in many cities, MODIFIER, the river in San A.

[RonPurewal]

Is it an issue to have a modifier in between the "Unlike X, Y" Structure (Unlike X, MODIFIER, Y)? Is there a need for "Y" to always be right next to "X"?

that ^^ is ok if "MODIFIER" is describing "X".

it's absoutely NOT ok if "MODIFIER" is describing "Y".

__

please do not attempt to invent your own answer choices for GMAC's problems. thanks.