^^ to the post above me
in that post, "it" refers to "rural migrant workers".
i can see what you're saying: yes, the pronoun is technically ambiguous. we are considering this problem for review.
HOWEVER,
it's important for you to realize that THE GMAT TOLERATES A CERTAIN DEGREE OF AMBIGUITY IN PRONOUNS.
there are only two ABSOLUTE RULES of pronouns:
* pronouns MUST match their intended antecedents in terms of SINGULAR / PLURAL (NO exceptions);
and
* pronouns MUST have an antecedent that is actually THERE in the sentence. (only one exception --> the idiomatic construction "it is ADJ that...", as in "it is unbelievable that he showed up early")
pronoun unambiguity, on the other hand, is a rule that is followed at best tenuously by the gmat people. therefore, you should only eliminate on pronoun ambiguity after you've taken care of other problems, unless the ambiguity is so fatal that you literally can't tell what the sentence is supposed to say.
for instance, if the sentence said "james talked with jim about his progress at work", then you can safely eliminate that one - because it's IMPOSSIBLE to tell to whom "his" refers.
Ron has been teaching various standardized tests for 20 years.
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