The warm ocean currents flow from the tropics to the Northern Hemisphere in the summer. The rays of the Sun strike the Northern Hemisphere more directly in the summer. The greenhouse effect increases in the Northern Hemisphere in the summer. The Northern Hemisphere is closer to the Sun in the summer.
I gave my students this multiple choice question: Which of the following statements best explains why the tilt of Earth on its axis causes summer to be warmer than winter in the Northern Hemisphere?

Only one answer is correct among these 4 choices:
- The warm ocean currents flow from the tropics to the Northern Hemisphere in the summer.
- The rays of the Sun strike the Northern Hemisphere more directly in the summer.
- The greenhouse effect increases in the Northern Hemisphere in the summer.
- The Northern Hemisphere is closer to the Sun in the summer.

Could you tell me which one is correct?

The rays of the Sun strike the Northern Hemisphere more directly in the summer.