The following diagram shows the cumulative abnormal returns (CAR) for oil exploration companies announcing oil discoveries over a 30-year period. Month 0 in the diagram is the announcement month. Assume that no other information is received and the stock market as a whole does not move. Is the diagram consistent with market efficiency? Why or whynot?

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15% 10% 5% -5% 6 -4 2 0 2 4 6 8 Time in months relative to event month