请教gwd 一道逻辑题

9-11 In general ,jobs are harder to get in times of economic recession because many businesses cut back operations.However ,any future recessions in Vargonia will probably not reduce the availability of teaching jobs at government -funded schools.This is because Vargonia has just introduced a legal requirementthat education in government-funded schools be available,free of charge ,to all Vargonian children regardless of the state of the economy ,and that current student-teacher ratios not be exceeded.

Which of the following ,if true ,most strengthens the argument ?

key : During recent periods when the Vargonian economy has been strong ,almost 25 percent of Vargonian children have attended privately funded schools,many of which charge substantial fees . 如何理解呢