Since the implementation of the president’s higher education subsidization policy at the beginning of this decade, the number of individuals entering the workforce with nothing but a high school diploma has decreased 5 percent. During that period, there has been a comparable increase in the number of individuals enrolled in four-year college programs. Clearly, the president’s policy has convinced and allowed many individuals to pursue higher education after earning their high school diplomas.
Which of the following, if true, casts the most serious doubt on the conclusion drawn above?
【选项】
An economic downturn has made it significantly more difficult to find a job immediately after earning a high school diploma.
选项是否正确？