Glucose gives positive Tollen's reagent due to the presence of a/an

Mutarotation is the change of specific rotation of aqueous solution of:

$\left(\mathrm{a}\right)$ $\mathrm{\beta }$- glucose from $+19.2°$ to $+52.5°$.

$\left(\mathrm{b}\right)$ $\mathrm{\alpha }$- glucose from $+111°$ to $+52.5^{°}$.

$\left(\mathrm{c}\right)$ a sucrose from dextrorotatory to laevorotatory.

Which of the following pairs of the compound are epimers?

$\left(\mathrm{a}\right)$ Glucose and mannose

$\left(\mathrm{b}\right)$ Mannose and galactose

$\left(\mathrm{c}\right)$ Glucose and galactose

$\left(\mathrm{d}\right)$ Mannitol and sorbitol