The correct answer is (b).
The sum of the interior angles of a polygon with $n$ sides is $(n-2)180^\circ$. A regular pentagon has $n=5$ sides, so the sum of its interior angles is $(5-2)180^\circ=540^\circ$. Each interior angle of a regular pentagon is therefore $540^\circ/5=108^\circ$.
Option (a) is incorrect because it is the measure of an exterior angle of a regular pentagon. An exterior angle of a polygon is the angle formed by one side of the polygon and the extension of an adjacent side. The measure of an exterior angle of a polygon is equal to the sum of the measures of the two interior angles that are not adjacent to it. In a regular pentagon, the measure of each exterior angle is $180^\circ-108^\circ=72^\circ$.
Option (c) is incorrect because it is the measure of a straight angle. A straight angle is an angle that measures $180^\circ$.
Option (d) is incorrect because it is the measure of a right angle. A right angle is an angle that measures $90^\circ$.