The significance of the Haymarket Square incident in 1886 was that. Select one:
A) the American socialist movement received a great boost.
B) the use of Pinkerton guards as strikebreakers was outlawed.
C) it stimulated a hysterical wave of fear of anarchism and its alleged connection with unionism.
D) it led to federal intervention in labor union matters.
E) unions won their demand for an eight-hour day.