The letter '$D$' in carbohydrates represents

Identify the glycosidic linkage present in lactose.

Considering the facts that
$I$. sucrose forms glycosidic linkage between $C_1$ of glucose and $C_2$ of fructose,while
$II$. lactose forms glycosidic linkage between $C_1$ of galactose and $C_4$ of glucose.
Choose the correct statement.

The correct representation in $6-$membered pyranose form for the following sugar $[X]$ is

Identify the sugar containing $\alpha, \beta-1,2-$ glycosidic linkage.

The formulas of $A$ and $B$ for the following reaction sequence are: