Which statement on the health of young people is TRUE?

a. Non-communicable diseases are a major cause of ill-health among adolescents living in high-income countries
b. The Youth2000 health and wellbeing survey is an example of a cohort study
c. Globally, most adolescents live in high-income countries
d. The disadvantage of using hand-held devices in the Youth 2000 surveys is that it may have caused less measurement bias