Please help need help asap

Donald is studying the eating habits of all students attending his school. he samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. he then collects data from the sample. which type of sampling is used? select the correct answer below: systematic sampling convenience sampling stratified sampling cluster sampling

What is the best definition of economic data?

Any study/memorization tips? i have exams in a week and it would be great to try suggestions!you ; )