Geometry

Question Analysis:
This question focuses on the classification of triangles based on angle measures, specifically identifying obtuse triangles.
The main focus is to test students' understanding of the definition of an obtuse triangle, which requires one angle to be greater than 90°.

Key Concept Explanation:
An obtuse triangle has one angle with a measure greater than 90° and the sum of all three interior angles of any triangle is always 180°.

Step - by - Step Solution:
Analyze option A: The angle 120° is greater than 90°, and 120° + 30°+ 30° = 180°. So, it is an obtuse triangle.
Analyze option B: The angle 95° is greater than 90°, and 95° + 40° + 45° = 180°. Thus, it is an obtuse triangle.
Analyze option C: The angle 100° is greater than 90°, and 100°+ 25° + 55° = 180°. Hence, it is an obtuse triangle.
Analyze option D: All angles 80°, 60°, and 40° are less than 90°. So, it is an acute triangle, not an obtuse one.