To prove that ΔDEF ≅ ΔDGF by SSS, what additional information is needed?

The triangles share side DF, so DF ≅ DF. The order ΔDEF ≅ ΔDGF pairs DE with DG and EF with GF; the shared side supplies the third pair, DF with DF. Therefore, the additional information needed for SSS is DE ≅ DG, choice C.

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