What else would need to be congruent to show that δjkl ≡ δmno by aas?
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a) lk ≡ on

b) ∠k ≡ ∠n
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c) lk ≡ om

d) ∠l ≡ ∠o

Following the given steps :

1. Since two corresponding angles are equal, the triangles are similar and angle B = angle Y. 

2. Now you can you can use ASA on (angle B, angleC, side BC) and (angle Y, angle Z, side YZ) 

From step 1
- C is true and doesn't need to be given;
- D was explicitly given as true.

Horizontal change or the change of x