Here's a problem to solve: Why is it winter in North America when it is summer in South America?

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

- A: The south is always warmer than the north.
 
- B: There is less land than water in the south.
 
- C: North America receives less direct sunlight during the winter.
 
- D: When it is December in North America, it is June in South America.
 