Correct answer: C
A) Before the actual first eruption on June 3, 1991, since early March, several other happenings occur such as earthquakes, phreatic eruptions, releasing of ashes, etc. that made the population aware of what was about to happen.
B) It affected the whole atmosphere and consequently the whole earth, having had effects throughout the whole world climate, agriculture, health, and other parameters.
D) It produced so many aerosols that's thought to be the largest eruption at emitting aerosols since Krakatoa's eruption.