based on the information marked in the diagram, △abc and △def must be congruent.\na. true\nb. false

Answer:

A. True

Explanation:

Step1: Identify right - angled triangles

Both $\triangle ABC$ and $\triangle DEF$ are right - angled triangles.

Step2: Check side - side congruence

We can see that $AC = DF$ (marked with one tick) and $BC=EF$ (right - angle sides). By the Hypotenuse - Leg (HL) congruence theorem for right - angled triangles (if the hypotenuse and one leg of a right - angled triangle are congruent to the hypotenuse and one leg of another right - angled triangle, the two triangles are congruent), or by Side - Angle - Side (SAS) congruence (right - angle is the included angle between the two marked sides), $\triangle ABC\cong\triangle DEF$.