Why Would Edith Be More Likely to Hire Her Teenage

Why would Edith be more likely to hire her teenage child than a landscaping firm to mow her lawn?  

A)  because the teenager is paid each time the lawn is mowed, but the landscaping firm bills Edith's credit card each month 
B)  because the teenager has a lower opportunity cost of mowing the lawn than the landscaping firm does 
C)  because the teenager is more likely to have the specialized tools necessary to complete the job quickly 
D)  because the teenager needs the money more than the landscaping firm