Because there is more oxygen in an alveolus (sac in the lung) than in the blood around it, oxygen diffuses

Because there is more oxygen in an alveoli sac than in the blood around it, oxygen diffuses from alveoli into capillaries. 

This is giving me a headache i have asked others and they don’t know it either

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.