The $\beta$ and $\alpha$ - D- glucose have different specific rotations. When either anomer is dissolved in water, their rotation change until the same fixed value results. What term is used for these changes?

Question

$\begin{array}{1 1}(a)\;\text{Absolute rotation}\\(b)\;\text{Optical rotation}\\(c)\;\text{Mutarotation}\\(d)\;\text{It is impossible to change the specific rotation}\end{array} $