Pure water has a ph of 7. the inside of a cell is also about ph 7. this might be so because buffers work best when the ph is close to 7. humans are largely made up of water by weight. most of the chemical reactions that occur in humans can proceed optimally at ph 7. ionic bonds cannot form at ph 7.

The pH of the blood is 7.4 and the pH of the human cells within is 6.8, that is, are both very near to neutral pH. The extreme values of pH, that is, either below or above 7.0 are generally regarded as not suitable for life.  

The majority of the species, involving humans, require to sustain pH within a fairly marginal range in order to survive. For example, the human blood requires to maintain its pH at about around 7.4. The buffer solutions that can resist the variations in pH are essential in sustaining stable hydrogen ion concentration in the biological frameworks .

i believe it would be c: tons.

the earth is thought to have been formed about 4.6 billion years ago by collisions from a cloud of hydrogen, helium, rock, ice and other materials. these were pulled together by gravity to form objects in and around earth like- asteroids and small early planets called planetesimals.

so, the best possible answer to this question will be option d- to harden materials to form different parts of earth’s layers