Change the narration: His father ordered him to go to his room and study.

His father said to him, "Go to your room and study."

His father said to him, "Go and study in your room."

His father said firmly, "Go and study in your room."

None of these

The indirect sentence is a command, so the direct speech should be an imperative sentence.

"His father ordered him to go..." becomes:

"His father said to him, 'Go to your room and study.'"

It preserves both the instruction and the original meaning accurately.