Select the correct active form.
"This error could have been avoided by careful planning."

Correct option is D

The correct active/passive voice of the given sentence is (d) Careful planning could have avoided this error.
Explanation (Voice conversion): The original sentence is in passive voice: This error (object) + could have been avoided (modal + perfect passive) + by careful planning (agent). To convert to active voice, make the agent “careful planning” the subject and keep the same modal-perfect structure with the main verb in V3: “Careful planning could have avoided this error.” The meaning and tense/aspect remain unchanged.
Structure:
· Passive Voice: Subject (object in active) + modal + have been + V3 + (by + agent)
· Active Voice: Agent/Doer + modal + have + V3 + object
· Active voice: Careful planning could have avoided this error.
· Passive voice: This error could have been avoided (by careful planning).
· Information booster: In passive with modals, modal + be/get + V3 is used (present/future), and modal + have been + V3 is used for perfect modal passives (e.g., could have been done, should have been completed).