The contrast drawn between the Haicheng earthquake in Paragraphs 2 and 3 and the Tangshan earthquake in Paragraph 3 contributes to a central idea that earthquakes are
А
all preceded by reliable signs, and therefore scientists have the ability to predict
earthquakes.
B
controlled by observable factors that just average citizens can report to the
authorities.
с
not always predictable, so new methods and more studies need to be
conducted
D
not often studied because there is no possible solution to the problem of
predicting earthquakes.