The correct answer is C. Increased support for the antiwar movement.
Explanation
The image shows a newspaper headline that mentions the assassination of four students from the University of Kent (Ohio) by National Guardsmen of that state. This was an event that occurred during the cold war, specifically during the Vietnam War, and is related to the antiwar movement that asked the Government of the United States of America for no intervention in that conflict. So, the assassination of this group resulted in increased support for the antiwar movement in the United States. According to the above, the correct answer is C.