Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Process | Main energy source for process |
| --- | --- |
| lightning | electricity |
| lunar cycle | gravity |
| water cycle | sunlight |
Question:
Gravity is the main energy source for what process? Select the correct choice to answer the question or fill in the blank.
Choices:
(A) Lightning
(B) Water Cycle
(C) Matter Cycle
(D) Lunar Cycle
Answer:
(D) Lunar Cycle