Which word group is a complete sentence?

The exciting end of the baseball game.

She did not understand what happened.

Two energetic women walking in the park.

Started his homework late Sunday night.

Question

Which word group is a complete sentence?       

       The exciting end of the baseball game.

       She did not understand what happened.

       Two energetic women walking in the park.

       Started his homework late Sunday night.

anonymous · Answer

"She did not understand what happened" would be the complete answer!
All the others are fragments, but this one names a subject, verb, and object specifically, which makes it a complete statement.