Final answer:
Triangles can be congruent either by the SSS criterion or the SAS criterion.
Step-by-step explanation:
Triangles can be congruent by either the SSS (Side-Side-Side) criterion or the SAS (Side-Angle-Side) criterion. SSS congruence states that if three sides of one triangle are equal to three sides of another triangle, then the two triangles are congruent. SAS congruence states that if two sides and the included angle of one triangle are equal to two sides and the included angle of another triangle, then the two triangles are congruent.