The graph below shows the average daily temperatures on January 1 from 1900 to 1934 for city A.

A graph shows the average daily temperature on the x-axis, and number of years on the y-axis, from 1 to 4. The average temperature was 18 for 2 years; 19 for 3 years; 20 for 2 years; 21 for 3 years; 22 for 2 years; 23 for 4 years; 24 for 3 years; 25 for 3 years; 26 for 5 years; 27 for 2 years; 28 for 1 year; 29 for 2 years; 30 for 2 years; 31 for 1 year.

The mean of the temperatures in the chart is 24° with a standard deviation of 4°. Which temperature is within one standard deviation of the mean?
16°
18°
27°
29°