If I'm remembering correctly, the First Continental Congress was a few years after the Boston Massacre and was prompted by the Coercive Acts, so it isn't D.
The tea party was also in response to the Tea Act, among other frustrations, so I don't think the answer is B either.
I believe that A refers to the battle at Lexington and Concord in 1775, but some people think that the first "shots" were during the Boston Massacre in 1770, so it could be A, but I don't know if that "officially" started anything.
If it isn't A I would guess C