A TV weatherman's end-of-year analysis of the local weather showed that among all the years for which records had been kept, the past year's average temperature had a z-score of 0.9. What does that mean?

A. The past year's average temperature was 0.9 higher than the historical mean.

B. The past year's average temperature was 0.9% higher than the historical mean.

C. The past year's average temperature was 0.9 standard deviation above the historical mean.

D. The past year's temperatures had a standard deviation of 0.9.