Correct Answer: Water covers most of Earth's surface.

Solution : The correct choice is the third option.

Active voice is the voice where the subject performs the action. When converting a sentence from the passive voice to the active voice, the subject performs the action rather than the action received by the subject.

The structure of the active voice in the case of the simple present tense is: "Singular subject + base form of the verb with the extension, i.e., s/es + object."

Therefore, the correct sentence would be: "Water covers most of Earth's surface."