Researchers wanted to study alcohol use by teenagers and observe if there were any differences between cohorts over time. They compared three groups of students (grades 6 to 8, grades 9 to 10, and grades 11 to 12) and focused on the frequency and amount of their alcohol use over a five-year period. They collected useful information about age-related changes, changes within the same individuals as they aged, and were able to account for the possibility of cohort and/or time of measurement effects. This is an example of .

Which is the best conclusion that can be drawn regarding the status of african-americans in the south in the late 1800s? a) african-americans made tremendous political, social, and economic advancements during the reconstruction era. b) passage of the 13th, 14th, and 15th amendments to the u.s. constitution guaranteed equal status and rights for all african-americans. c) the reconstruction policies enacted by the federal government were highly effective in african-american citizens transition to life after slavery. d) although african-americans had equal rights under federal law they were still economically, politically, and socially inferior to whites in the south during the reconstruction era.