The correct answer is D.
The My Lai Massacre occured in 1968, but did cause outrage among US citizens since the US killed unarmed Vietnamese citizens.
The Bay of Pigs Invasion occured in 1961.
The Gulf of Tonkin Resolution was signed in 1964.
This shows that the only correct answer based on the time frame provided in the question is D. This invasion of Cambodia lead to several different protests across the country, including the famous Kent State protest.
