Answer:
C) Experiment
Explanation:
With a controlled experiment, a researcher can use a student batch that studied the old curriculum as a control group, and the new batch of students as the 'test' group. To measure student achievement, the researcher would need to either:
1. compare test results for the 2 groups
2. do a longitudinal study - follow the 2 groups of students across several years, and track their 'achievements' (university admissions, jobs, income, etc)
With the other 3 options, the results wouldn't necessarily be accurate or relevant.