Correct Answer: The commander said to the soldiers, “Climb the hill.”

Solution : The correct choice is the fourth option.

The steps to conversion are as follows:

• Change the sentence in an indirect speech from imperative to assertive.
• The tense of reported speech is changed only when the reporting verb is in the past tense.
• The reporting verb "ordered" is changed to "said".
• "To infinitive" is removed. "To climb" is changed to "climb".
• The words of the speaker are enclosed in the inverted commas.

Therefore, the direct form would be: The commander said to the soldiers, “Climb the hill.”