Answer:
d. They differed little on the central issue of Vietnam.
Explanation:
One of the most important topics during the 1968 campaign was the subject of the war in Vietnam. By 1968, the country had grown tired of the war and was seeking a way out. Humphrey was considered to be close to the war and connected to the "old politics" that allowed it to happen. However, there was little evidence to substantiate this. During the campaign, Humphrey emphasized his desire to end the war. In the end, Humphrey and Nixon differed little on the central issue of Vietnam.