The Proportion of American High School Students Holding Part-Time Jobs

The proportion of American high school students holding part-time jobs has decreased over the past two decades. Which of the following is an explanation for this?

A) Parental expectations have changed, and parents no longer feel it is necessary for teenagers to work.
B) Fewer and fewer high school graduates are seeking college admission.
C) The recession during the first decade of the twenty-first century left many adults without jobs.
D) So many teenagers want part-time jobs that there is too much competition for too few jobs.