The quantity $s^2_p$ is called the pooled variance estimate of the common variance of two unknown but equal population variances. It is the weighted average of the two sample variances, where the weights represent the:
A. sample standard deviations
B. sample sizes
C. degrees of freedom for each sample
D. sample variances

The number of degrees of freedom associated with the t test, when the data are gathered from a matched pairs experiment with 10 pairs, is:
A. 9
B. 18
C. 10
D. 20