C中in the period before the last economic recession, 指经济还没坏的时候. 那么现在(没有经济萧条的时候)的老师人数超过那时的20% (Nearly 20 percent more teachers are currently employed in Vargonia’s government-funded schools than had been employed), 也就意味着 ==> 教师人数没有因为recession而减少, 从而支持argument.
I vote C。Because "Nearly 20 percent more teachers are currently employed in Vargonia’s government-funded schools than had been employed in those schools in the period before the last economic recession."==>After a economic recession, the number of teachers increased ====>Any future recessions in Vargonia will probably not reduce the availability of teaching jobs at government-funded schools.
before recession, the teacher numer is less than the number after recession. which means that recession create job opportunities whereas reduce job opportunity. Therefore , C support the argument