Virtually all aircraft fly in which two layers of the atmosphere?

The correct answer identifies the troposphere and stratosphere as the two layers of the atmosphere where virtually all aircraft operate.

The troposphere is the lowest layer of Earth's atmosphere, extending from the surface up to about 8 to 15 kilometers (5 to 9 miles) depending on latitude and weather conditions. This layer contains most of the atmosphere’s mass and is where all weather phenomena occur. It is the primary airspace in which commercial flight and general aviation take place due to its favorable conditions for flight and sufficient oxygen availability.

Above the troposphere is the stratosphere, which extends to approximately 50 kilometers (31 miles) above the Earth's surface. Aircraft occasionally operate in the lower stratosphere, particularly those on long-haul flights that utilize the jet stream for more efficient travel paths. The stratosphere is also where the ozone layer resides, absorbing most of the sun's harmful ultraviolet radiation.

Together, these two layers provide the necessary conditions for safe and efficient aircraft operation, making them the primary focus for aviation.