Official Explanation
The credited answer is (B). If number of union employees went up, but the percent of union employees stayed the same, this means the total number of employees had to go up in this period.
We don't know whether the union membership rose continuously, a rise from 2008 to 2009, then another rise from 2009 to 2010; or whether it went down a bit in 2009 and then shot up in 2010. Either could be true, we have no grounds for concluding that 2009 was higher than 2008. Choice (A) is incorrect.
We have no idea what the union dues structure was, and how it might have changed from 2008 to 2010. If dues were exactly the same, then more members would produce more revenue in dues. We don't know, though, whether dues stayed the same or changed. Choice (C) is incorrect.
Choice (D) is much much too broad. We have information about one factory. There is no way we can deduce something about every factory in the sector, factories all over the country. Choice (D) is incorrect.
If the percentage of union employees stayed the same, then the percent of non-union employees also would have had to have stayed the same. If there were more union members, then that means there were more employees overall, which means there would also have to be more non-union members. Choice (E) is incorrect.
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