The cup like structure, in which the femur fits into the hip bone is known as Acetabulum.
the acetabulum is referred to a concave shapoed surface of the pelvis, which have a cup like groove. This groove helps in the binding of the femur head to the hip or the pelvic bone.
The round head of the femur gets fits into this cup shaped structure and forms the hip joint. The acetabulum is formed by the contribution of ischium, ilium and the pubis.
Sand is granular and coarse meaning that water and nutrients can flow through it quite easily. Clay on the other hand has very fine particles that cling together to form a waterproof substance which traps/ stops any nutrients or water from moving down. Clay's also quite difficult for plants to get their roots into. Silt has a texture between clay and sand, meaning that it is the ideal substance as it allows the best water and nutrition movement in the soil. Most plants will grow best in silt, but there are some plants who are more adapted to living in sand (e.g. Marram grass) or clay.
A river that comes from rain, glaicers etc would be a good example of fresh water rivers. Cause the water is coming from something that is most likely been unthouched by man or has been filterd and cleaned from minerals in the ground.
They saw how smoking effected the body since smoking was pushed as something good for a long time, a lot of people started smoking and after a few years doctors finally saw a difference between a smokers body and a non smokers body
Till this day We are always learning more and more so I think this can be helpful for future vaccines of diseases
