An ecosystem cannot repair itself after a volcanic eruption. after a flood. after a tornado. after a housing development is built.

The correct answer would be after a housing development is built.

The other options like a volcanic eruption, flood, and tornado come under natural calamities which adversely affect the ecosystem and greatly reduce the population of species living there.

However, they do not eliminate the complete ecosystem. The damaged ecosystem undergoes secondary succession and repairs itself to produce a similar ecosystem that existed before the natural disaster.

In contrast, housing development (man-made changes) leads to the permanent loss of the natural habitat of wild animals and plants.

It is why an ecosystem can not repair itself after a housing development is built.

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

hope its .

i think the answer is b.