A study in country A used the expansion of compulsory education from 8 to 9 years as an instrument to study the impact of education on wages. The ESLS coefficient on years of education would estimate: (3 a. The average impact of a year of education on wages. (3 b. The average impact of a year of education on wages only for the type of individual who would have 8 years of education before the expansion. ( 3 c. The average impact of the 91h year of education on wages. The expansion of compulsory education in country A happened in 1995. Which aspect is not important to assess the external validity of the study for country B right now? i 3 a. Country B now has a much higher unemployment rate than country A had around \"I995, so their labor markets are not comparable. ('3 b. Labor market for those finishing school in 1995 was very different from the labor market faced by school graduates today and hence the impact of one additional year of education may not be the same. (3 c. Individuals in the two consecutive cohorts used in the study in country A were similar and faced similar labor market conditions. Hence, the treatment and control groups were comparable