Fusion of hydrogen is the main source of the sun's energy.

True False

True

Explanation:

Fusion of hydrogen is the main source of the sun's energy.

The primary source of solar energy, and that of similar size stars, is the fusion of hydrogen to form helium (the proton–proton chain reaction), which occurs at a solar-core temperature of 14 million kelvin.

so I think true

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.