单项选择题

It is more difficult to be a parent today because

A.today's children are not obedient and they think their parents' warnings are of no value.
B.today's parents are so busy working that they have no time to take care of their children.
C.today's parents have to keep their children from too many distractions and bad influence.
D.today's teachers fail to do their work well and set bad examples for students.