The correct answer is D) Kent State University protests.
The Kent State protests were just one example of several that happened during the late 1960's and early 1970's. These protests on college campuses usually revolved around America's involvement in Vietnam or other nearby countries (like Cambodia). These protests were often peaceful, however the Kent State protest is studied because the college students got into a heated exchange with the National Guard. The refusal of this group of students to disperse and the rumored throwing of objects at the National Guard resulted in gunfire and multiple students killed.