Geometry

Question Analysis:
This problem involves completing a proof by contradiction.
The main focus is identifying the correct assumption that opposes the conclusion of the original statement.

Key Concept Explanation:
In proof by contradiction, you assume the opposite of what you want to prove, then find a logical conflict.

Step-by-Step Solution:
Original statement: "They cannot form a triangle."
Opposite assumption: "They can form a triangle."
This leads to a contradiction using triangle inequality.
Therefore, original statement must be true.

Option Analysis:
A. ❌ Adds extra info not in original claim
B. ❌ Restates original claim, not the opposite
C. ✅ Correct assumption (opposite of the conclusion)