Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- A: The warm ocean currents flow from the tropics to the Northern Hemisphere in the summer.
 
- B: The rays of the Sun strike the Northern Hemisphere more directly in the summer.
 
- C: The greenhouse effect increases in the Northern Hemisphere in the summer.
 
- D: The Northern Hemisphere is closer to the Sun in the summer.
 