Billy is nine years old. his mother allows him to walk to school on his own. what

D. not caring for her child enough. A mother should always walk with her child when they're 9. 

A mother should care for her child no matter what. Even if they know that the child will hate them for it. 
It's good to teach them indepence, as you don't want them to always ask you for help for everything... but that'll be too early. 
I don't see how discipling make sense, you should never discipline by letting the child walk to school on their own, more like take something away or something that will not get them killed/injured. 

Hope I helped! 

No, only newborns should use ear tubes, because their ear holes are bigger than people from the ages between 50-65 because by the ages between 50-65 it would be too small for the tube to be able to go in.