Given the figure below what conclusion and reason can be made?
\angle7∠7

A. C: E is the midpoint

R: Definition of Midpoint

B. C: DE = EF, then DF – DE = DF – EF

R: Subtraction Property of Equality(SPE)

C. C: DE = EF

R: Definition of Congruent Segments

D. C: DE + EF = DF

R: Segment Addition Postulate