DrArrabella Surveyed Students in His Finance Class About Their Attitudes

Dr.Arrabella surveyed students in his finance class about their attitudes concerning the Canada Pension Plan and concluded that young adults across Canada doubt that they will ever receive Canada Pension benefits.Why might his conclusion be flawed

A)  He knew his subjects before he surveyed them. 
B)  His students were not a representative sample of young adults. 
C)  He did not survey the entire population of young adults. 
D)  His students were a random sample.