The Moon must be full. The Moon must be waxing. It must be the beginning of the month. It must be winter in the Northern Hemisphere.
I gave my students this multiple choice question: Which of the following is a necessary condition for a lunar eclipse to occur?

Only one answer is correct among these 4 choices:
- The Moon must be full.
- The Moon must be waxing.
- It must be the beginning of the month.
- It must be winter in the Northern Hemisphere.

Could you tell me which one is correct?

The Moon must be full.