The variable is independent because you are affecting it by changing it individually. It would be dependent if you changed one variable then the water was affected.
Answer:
Photosynthesis occurs in the chloroplast
The integumentary system (skin) reacts different on different sun intensity (different length exposure to sun).
For example, moderate exposure to the sunlight contributes to the production of melanin and vitamin D by the body. On the other hand, high exposure to sunlight can have negative health effects such as sunburn, which is an inflammatory response to DNA damage caused by UV radiation.
I just took the test, the answer is weathering.