I don't know if their is sopposed to be options but my best educated guess is "Natural"
When stem cells grown on hard, rigid surface, then they became bone cells. Researchers demonstrate in Nature materials that human mesenchymal stem cells grown on a rigid substrate for some time become biased toward differentiating into bone-cell lineage, whereas cell grown on softer surfaces are just likely to eventually follow a bone or fat cell fate.
Explanation:
Each D-T fusion event releases 17.6 MeV (2.8 x 10-12 joule, compared with 200 MeV for a U-235 fission and 3-4 MeV for D-D fusion). On a mass basis, the D-T fusion reaction releases over four times as much energy as uranium fission. :):)
I'd say A: tidal waves. B, C, and D don't really seem to fit for me.
