Q. Change the voice: The watchman switched on the lights before it began to grow dark.

• (A) The lights were only switched on before it began to grow dark.
• (B) The lights are being switched on before it began to grow dark.
• (C) The lights were being switched on by the watchman before it began to grow dark.
• (D) The lights were switched on by the watchman before it began to grow dark.