High school students who feel that they are not succeeding in school often drop out before graduating and go to work. Last year, however, the city' s high school dropout rate was significantly lower than the previous year' s rate. This is encouraging evidence that the program instituted two years ago to improve the morale of high school students has begun to take effect to reduce dropouts. Which one of the following, if true about the last year, most seriously weakens the argument? ['The morale of students who dropped out of high school had been low even before they reached high school.', 'There was a recession that caused a high level of unemployment in the city.', "The antidropout program was primarily aimed at improving students' morale in those high schools with the highest dropout rates.", 'As in the preceding year, more high school students remained in school than dropped out.']