There is not enough light being reflected off the person in the room. Light rays cannot pass through a window twice. Outside light does not pass through windows. Sunlight is not as intense as other sources of light.
I gave my students this multiple choice question: A person in a dark room looking through a window can clearly see a person outside in the daylight. But a person outside cannot see the person inside. Why does this happen?

Only one answer is correct among these 4 choices:
- There is not enough light being reflected off the person in the room.
- Light rays cannot pass through a window twice.
- Outside light does not pass through windows.
- Sunlight is not as intense as other sources of light.

Could you tell me which one is correct?

There is not enough light being reflected off the person in the room.