The chart gives data on greenhouse gas emissions in the united States from 1990 to 2013. What questions help clarify the evidence in the chart?

Answer:
hello guys,
so my ANSWERS to this question are :
3# and 4#
Why two? because it said questions ( plural ) and why these questions because as the person below said its better if its why question and not what is going on in this graph.
And personally questions that could help clarify the elements in the graph are these questions :
1. Why are carbon dioxide emissions so much higher than other greenhouse gases?
- it's a real question that could help us understand the graph
2. Why did the quantity of carbon dioxide emissions stay constant throughout the period?
- actually why, help us understand the chart or clarify it...
( optional : What percentage of total greenhouse gas emissions is caused by natural sources?
this question is also very interesting but i ain't not sure... so you do you, and again put the questions you feel the more comfortable with )...
- shay