The present day continent of north america was part of 200 million years ago. a. laurasiab. gondwanaland c. neither laurasia nor gondwanaland

Option (A)

Explanation:

The earth's crust is comprised of the lithospheric plate and they are constantly in motion over the viscous layer of asthenosphere due to the generation of convection current in the mantle. It is due to the heat radiated from the interior of the earth.  

These plates were once all together forming a supercontinent named Pangaea. This Pangaea got separated into Laurasia and Gondwanaland.

North America was formed from the separation of the Laurasia about 200 million years back.

This plate motion was proved by some of the evidence put forwarded by Alfred Wegener. The continental drift theory that was modified to Plate tectonic theory was able to explain the mechanism behind this plate motion.

Hence, the correct answer is option (A).

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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