The Difference Between the Denominator of the Z Statistic and That

The difference between the denominator of the z statistic and that of the single-sample t statistic is that in a:

A) z statistic we divide by the actual population standard error (s_M) , but in a t statistic we divide by the estimated standard error ( $\sigma$ _M) .
B) z statistic we divide by the actual population standard error ( $\sigma$ _M) , but in a t statistic we divide by the estimated standard error (s_M) .
C) t statistic we divide by the actual population standard error (s_M) , but in a z statistic we divide by the estimated standard error ( $\sigma$ _M) .
D) t statistic we divide by the actual population standard error ( $\sigma$ _M) , but in a z statistic we divide by the estimated standard error (s_M) .