The correct answer is (c).
The sum of the three interior angles of a triangle is always 180°. Therefore, if one of the angles is 100°, the other two angles must add up to 80°. The angle bisectors of two angles of a triangle divide the angles into two equal parts. Therefore, the angle between the angle bisectors of the other two angles is 120°.
Option (a) is incorrect because the sum of the three interior angles of a triangle is always 180°. Therefore, if one of the angles is 100°, the other two angles must add up to 80°. The angle bisectors of two angles of a triangle divide the angles into two equal parts. Therefore, the angle between the angle bisectors of the other two angles is 120°, not 80°.
Option (b) is incorrect because the angle between the angle bisectors of the other two angles is 120°, not 100°.
Option (d) is incorrect because the angle between the angle bisectors of the other two angles is 120°, not 140°.