Collective nouns can be subtle, because you have to tap into the MEANING of the sentence. Specifically,
* if the sentence stresses the uniformity or 'togetherness' of the group, then use the singular;
* if the sentence stresses individual actions (perhaps grouped together, but still regarded as clearly individual), then go with the plural.
* WHEN IN DOUBT, GO SINGULAR (this won't work 100% of the time, of course, but we find that most of these things - especially on the GMAT - are slanted toward the singular.)
Examples:
The faculty always votes for tuition hikes at the annual meetings. (singular, because the faculty is portrayed as voting AS A BLOC or UNIT)
The faculty commute very long distances from their homes to the campus. (plural, because, although all the faculty members commute, there is still an obvious individualism to their commuting)
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