Three reasons why earth is a unique planet ?

First it has the right amount of water, second earth has the right amount of oxygen, last is that it is not to close or far from the sun.

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.

b. to discover aspects of the natural world.

hopefully i .