Give a brief general description of the number of degrees of freedom.
a. the number of degrees of freedom for a collection of sample data is the number of sample values that are determined after certain restrictions have been imposed on all data values.
b. the number of degrees of freedom for a collection of sample data is the total number of sample values.
c. the number of degrees of freedom for a collection of sample data is the number of unique, non-repeated sample values.
d. the number of degrees of freedom for a collection of sample data is the number of sample values that can vary after certain restrictions have been imposed on all data values.