Geometry

Question Analysis:
This question combines the concepts of isosceles triangle classification based on side lengths and acute - triangle classification based on angle measures.
The main focus is to test students' ability to apply both classification criteria simultaneously.

Key Concept Explanation:
An isosceles triangle has at least two equal side lengths.
An acute - triangle has all angles less than 90°.

Step - by - Step Solution:
Analyze option A: It has two side lengths of 4 cm, so it is isosceles. Also, all angles 70°, 70°, and 40° are less than 90°, so it is acute. Thus, it meets both criteria.
Analyze option B: All side lengths are 6 cm, making it isosceles (and equilateral, which is a special case of isosceles). All angles 60°, 60°, and 60° are less than 90°, so it is acute. It meets both criteria.
Analyze option C: The side lengths 3 cm, 4 cm, 5 cm form a right - triangle (by the Pythagorean theorem), so it is not acute. It is also not isosceles as all sides are different.
Analyze option D: It has two side lengths of 5 cm, s...