Which of the following is visible to o a person only because light from another source reflects that off of it?

Clouds

Explanation:

The cloud among the given options would be visible only when the light from a different source reflects outside it. This is due to the reason as we are able to see the clouds only when the sun reflects it's light on it and we can witness it by not seeing the clouds in the sky on a shady day. Thus, option D is the correct answer. Sun cannot be the one as the sun itself can produce its own light and thus, a source of light. The lightning is characterized as a 'flash of light' and the flashlight also produces light.