a man is using an axe to chop down a tree. After a short time after the axe hits with tree the man hears a clear echo he estimates that the echo is 3 seconds after the axe hits the tree. suggest what type of obstacle might have caused such a clear echo​

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:

as we probably am aware that our atmosphere or air have various levels, each level has different gasses, and each gas has another porousness. at the point when the light originates from lower porousness to higher penetrability, it alters its course. with the goal that implies that when the light originates from the moon to the earth, it alters it's course a lot more occasions. it essentially implies that the state of the light piece of the moon is changed on the earth.

not copied too! hope this !

joke:

h o h o hope you have a merry christmas!

e/c, where e is its total energy

the answer is 12 as i may remember

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