At Shiprock, New Mexico, a perenially

[tim]

please read the whole thread. Stacey explained this in October 2007..

[thanghnvn]

Generally "where" is used for physical locations - otherwise, we have to use a variant such as "in which." Other variants include "at which" and "for which." Both "where" and "in which" refer to the community, which has already been established as a physical location (Shiprock New Mexico), so we can use "where." We could also use "in which" - this just means "in the community" which is also grammatically correct.

The key is that the only "in which" option given has a pronoun error, so I don't have a grammatically correct option that uses "in which." That leaves me with "where" by default.

A, B, and E all have pronoun errors. D would have to have a comma before the which and the verb "has" makes the sentence awkward. The community doesn't "have" household incomes. The individual members of the community do.

thank you, Stacey
you said that D need comma before "which".
from this, I understand that "which clause" on gmat alway shows non restrictive information. this is different from general grammar in which "which clause" can be used with or without a comma, depending on weather the meaing is restrictive or non restritive.

is my thinking correct? pls confirm

[tim]

that's correct. remember, whenever GMAT grammar rules differ from what you've learned elsewhere you just need to learn the GMAT rule because they're the ones who administer the test.. :)