The astronomical object known as crab nebula is thhe remnant of an exploded star. the explosion was seen by the chinese in 1054 c. e. however, the crab nebula is about 3500 ly distance from the earth in what year did the star actually explode.

cell differentiation  is how generic embryonic  cells  become specialized  cells. this occurs  through a process called gene expression. gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and this is what dictates how a  cell  functions.

explanation:

b.transmitters send radio waves, and receivers capture radio waves.