The correct answer is D.
Standard deviation is a measure of how spread out numbers are in a data set. A lower standard deviation indicates that the data points tend to be very close to the mean, while a higher standard deviation indicates that the data points are spread out over a wider range of values.
A tighter probability distribution is one in which the data points are more closely clustered around the mean. This means that the standard deviation of a tighter probability distribution will be smaller than the standard deviation of a wider probability distribution.
Option A is incorrect because standard deviation is not a measure of time.
Option B is incorrect because standard deviation is not a measure of risk.
Option C is incorrect because standard deviation is not a measure of how likely an event is to occur.