In order to strengthen this argument, which should the author consider adding

The correct answer is D) survey results that indicate students who did have to complete service hour requirements felt the requirement was a positive and beneficial experience.

The other options of the question were A) humorous anecdotes to lighten the mood and gently criticize opponents. B) an attack against administrators and community leaders who do not support this idea. C) a stronger worded plea that begs the reader to agree to require service hours because it's the right thing to do.

In order to strengthen this argument, the author should consider adding survey results that indicate students who did have to complete service hour requirements felt the requirement was a positive and beneficial experience.  

This way the author is going to include all possible information that serves to demonstrate and support what it is stating. Those survey results are a way good to demonstrate the student's satisfaction for having taken service hours. The survey is a quantitative evaluation that strengthens the author's arguments.

typical characteristics of global cities include all of the following except being culturally isolationist.

explanation: