Question:  _______________ have become increasingly necessary as the incidence of crises has increased. This appears to be due to an increasing number of simple managerial mistakes, incorrect decision making, technology failures, and uncontrollable events in the external environment.
A: Crisis communications.
B: Advertising.
C: Public relations.
D: Viral marketing.
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option. There should be exactly 7 paragraphs separated by the markdown divider: ***.
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