challenge: What event in 1968 is considered to have culminated in the protest at the Three Cultures Plaza in Tlatelolco?
  
  A. The founding of the Colegio Isaac Ochoterena
  B. The anniversary of Isaac Ochoterena's death
  C. The student unrest and confrontations in July
  D. The opening of a new vocational school in Mexico City
  Answer: 