Water Cycle Which of these best describes what is happening at arrow 1 in the water cycle?
A Water vapor is collecting to form clouds.
B Water falling as rain is changing into clouds.
Water is flowing into the ocean.
D Water heated by the sun is changing to water vapor.

Water heated by the sun is changing to water vapor.

D

Explanation:

It is one state of water within the hydrosphere. ... Water vapor is transparent, like most constituents of the atmosphere. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation.Condensation is the process where water vapor becomes liquid. It is the reverse of evaporation, where liquid water becomes a vapor

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

read more on -

the generally accepted parts of modern cell theory include: all known living things are made up of one or more cells. all living cells arise from pre-existing cells by division. the cell is the fundamental unit of structure and function in all living organisms.