Question

Given: AD = CF
BC = DE

Prove: AB = EF

Statement Reason
1. AD = CF given
2. AD = AB + BC + CD
CF = CD + DE + EF

segment addition
3. AB + BC + CD = CD + DE + EF Transitive Property of Equality
4. AB + BC = DE + EF
5. BC = DE given
6. AB = EF Subtraction Property of Equality

What is the reason for the fourth statement in this proof?

A.
definition of collinear points

B.
segment addition

C.
Subtraction Property of Equality

D.
Substitution Property of Equality