Why are chemical changes considered “unseen”?

The crust of earth may a- continets and ocean floors. b-continents only. c-layers of sedimentary rocks and continents. d-all of the above

How does blood clotting prevent the entry of pathogens through cuts and wounds? answer asap,, this is due tomorrow. will mark as brainliest or whatever you call it : )

28. which is not a reason that water is used to store spent fuel rods from nuclear power plants? water increases the speed of the chain reaction in the fuel rods. water protects nuclear power plant workers from the high temperature and radiation of the fuel rods. water acts as a radiation shield to reduce the radiation levels. water cools the spent rods. salts action