Which is a form of active transport? proteins push molecules through the cell membrane. proteins create openings on another side of the cell membrane. proteins open up channels in the cell membrane. proteins enter and exit the cell freely.

The correct option is this: PROTEINS PUSH MOLECULES THROUGH THE CELL MEMBRANE.
An active transport is a type of transport in the living system, which requires an energy to occur, because the movement  of the molecule involved is usually against the concentration gradient. The energy form used in this case is ATP. Active transport usually requires carrier proteins. 

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.