100 POINTS PLEASE ANSWER- the answer is not c or d CONFIRMED The diagram illustrates the process of developing genetically modified corn.

What occurs at step 3 in the diagram?
The restriction enzymes cut the isolated DNA into fragments.
The gene of interest is inserted into an expression cassette.
The recombinant DNA is inserted into the host cell nucleus via a vector.
The expression cassette is inserted into a plasmid for cloning.

It is a, restriction enzymes cut the isolated DNA into fragments.

Explanation:

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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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a- all cells come from pre-existing cells