The reason why we have nuclear radiation is because of:

Radiation can arise from human activities or from natural sources. Most radiation exposure is from natural sources. These include: radioactivity in rocks and soil of the Earth's crust; radon, a radioactive gas given out by many volcanic rocks and uranium ore; and cosmic radiation.

O Trails and greenways allow people to exercise in a safe and inexpensive manner

Explanation:

Greenways are corridors of protected open green spaces which have been created for conservation and/or recreation purposes. Moreover, trails also provide excellent options for transportation and recreation that reduce air pollution, thereby promoting the development of safe and livable communities. Both trails and greenways are ecologically friendly alternatives to make exercise and maintain a healthy lifestyle, helping communities in creating good and safe places to live, where children can safely walk or bike to and from school.