Build several models of his tree house out of different materials, and see which model holds up best to wind, water, and ice.
One example: The improvement in science and technology over the years has decreased the infant mortality rate. Since more babies live, we have a higher population.
Also, with increases in science and technology, there are many diseases that were once considered fatal that are now easily treated. This has also led to a higher population.
The correct answer is (B) Photosynthesis and diffusion from the air
Dissolved oxygen enters the water from photosynthesis and through air. The The aeration of water can be caused by wind. From the air oxygen diffuse into the water and gets mixed in the it through circulation. The oxygen is also produced as a waste product of photosynthesis from blue-green algae, phytoplankton, etc which is added in water.