The last one is the correct answer.
The mean is exactly 0.5 (where the peak of the graph occurs), so the second option is false.
Each dotted line to the left or right of the mean is supposed to indicate a certain number of standard deviations away from the mean. (e.g. the line between 0.3 and 0.4 is one standard deviation away from the mean, while the line at 0.2 is two standard deviations away). This means the standard deviation must be 0.15, since [tex]0.5-2\times0.15=0.2[/tex], so the first option is also false.
0.7 clearly lies between one and two standard deviations from the mean, so the third option is false.
