Geometry

Question Analysis:
This higher-level question assesses the ability to identify missing elements in a proof context.

Key Concept Explanation:
For SAS, the equal angles must be between the specified sides.
The proof requires confirmation that ∠C is between AC & BC, and ∠F is between DF & EF.

Step-by-Step Solution:
Given elements:
AC = DF (Side)
BC = EF (Side)
∠C = ∠F (Angle)
Missing verification:
Are ∠C and ∠F between the given sides?
Conclusion:
The critical missing information is confirmation that these are included angles.

Option Analysis:
(A) Unnecessary - AB = DE would make it SSS
(B) Irrelevant - Doesn't help establish SAS
(C) Unhelpful - Doesn't verify angle position
(D) Correct - Complet...