**Solution:**

BS=BE+ES=ST+ES=ET

BA=DT (given)

Thus, is congruent to (RHS)

Hence

Thus DT//BA (alt. angles)

(Proved)

By Pythagoras’ Theorem, we have

Hence and are congruent (SSS).

Hence

Thus DB//TA (alt. angles)

Therefore, ABDT is a parallelogram since it has two pairs of parallel sides.

(shown)