The Following Information Was Obtained from Matched Samples Taken from Two

The following information was obtained from matched samples taken from two populations. The daily production rates for a sample of workers before and after a training program are shown below.Assume the population of differences is normally distributed. $\begin{array}{lll}\text { Worker } & \text { Before } & \text { After } \\1 & 20 & 22 \\2 & 25 & 23 \\3 & 27 & 27 \\4 & 23 & 20 \\5 & 22 & 25 \\6 & 20 & 19 \\7 & 17 & 18\end{array}$
The point estimate for the difference between the means of the two populations is

A) -1.
B) -2.
C) 0.
D) 1.