Final answer:
The atmosphere is a region of unevenly mixed gases, 50 to 300 miles above the Earth's surface. Therefore, the correct option is c. atmosphere.
Step-by-step explanation:
The correct answer is c. atmosphere. The atmosphere is the gaseous layer that surrounds a planet, and it consists of a mixture of gases including nitrogen, oxygen, and minor elements. It can be subdivided into different regions, such as the exosphere, thermosphere, mesosphere, stratosphere, and troposphere. The troposphere is the lowest layer of the atmosphere, extending up to about 12 km above sea level and is where most weather events originate.