The obligations of citizenship in the us are not mandatory.

The obligations of citizenship in the US ARE MANDATORY!! If you come here illegally you will be deported. Our new president is very good with immigration and only allows certain people to come in. That is a privilege, so you should come here and do what we ask.  Hope this helps!

The correct answer is D. Drivers of the mail train

They are characters from the Call of the Wild, famous novel by Jack London.