Answer:
The best addition for providing commentary on the quotation from President Obama is:
A. This imagery provides evidence of the catastrophe and builds sympathy for the people and for the president's plan to use force.
Step-by-step explanation:
The excerpt in the attachment ends with a quote from the president's speech. It contains imagery, a literary and rhetorical device that helps describe images vividly. The president's purpose in describing the dead bodies is to convince people to accept the use of force against the use of chemical weapons by appealing to their emotions - sadness, sympathy, horror, etc.
With that in mind, we can safely choose letter A as the best addition to the excerpt:
A. This imagery provides evidence of the catastrophe and builds sympathy for the people and for the president's plan to use force.