Cyanobacteria, once referred to as blue-green algae, has a fossil record that dates back nearly 3.5 billion years and is among the oldest fossils known. the cyanobacteria/ blue-green algae had cell walls and were photosynthetic. a few hundred years ago, this organism was classified as a plant, then as a protist. today it is classified in the eubacteria because it
a) is photosynthetic.
b) is know to be prokaryotic.
c) is the ancestor of land plants.
d) has cellulose cell walls and chloroplasts.

the answer is D

Explanation:

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.  

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b. to discover aspects of the natural world.

hopefully i .