Researchers studied the mean egg length (in millimeters) for a bird population. After taking a random sample of eggs, they obtained a 95% confidence interval of (45,60). What is the value of the sample mean? Choose the correct answer below.
A. 15.0 mm
B. 52.5 mm
C. 7.5 mm
D. Somewhere between 45mm and 60mm, but the exact value cannot be determined without more information.