Explanation: Xiaohua’s thinking is incorrect, because AC and BD are not the sides of these two triangles;

The correct answer is: connect BC,

In △ABC and △DBC,

AB=CD (known) AC=BD (known) BC=BC (common side),

∴△ABC ≌△DBC (SSS);

∴∠A=∠D,

In △AOB and △DOC,

∵∠A=∠D( Proved) ∠AOB = ∠DOC (opposite angles are equal) AB = CD (known),

∴△AOB≌△DOC (AAS).