The solar system is considered a natural system because it was made and controlled by natural forces, meaning, it was never influenced with human creations. It is considered as one of the products of the phenomenon of the physical world. Hope this answer helps you.
I would say D. small intestine
If you want an explanation, here it is
After leaving the stomach, water is absorbed mostly in the early segments of the
small intestine, the duodenum, and the jejunum. A small portion of all water absorption occurs in the stomach and the colon: the small intestine absorbs 6.5L/day, whereas the colon absorbs 1.3L/day.
The G1 phase is a period in the cell cycle during interphase that happens after cytokinesis.
