The diagram that would support his plan to use ASA is option A.
"Angle-Side-Angle," is a criterion used to prove that two triangles are congruent. If two triangles have two angles and the included side of one triangle equal to the corresponding two angles and the included side of another triangle, then the triangles are congruent according to the ASA postulate.
In general, congruent triangles have the same shape and size, and proving congruence is essential in geometry to establish relationships between various geometric figures. The diagram that would support his plan to use ASA is option A.