Many endurance athletes train at high altitudes before a major sporting event. They do this because they think that training at high altitude changes the number of red blood cells in their body.

Describe an investigation to find out if training at high altitude
does change the number of red blood cells in the human body.
(What are the control variables?)

Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.