Amixture that appears to contain only one substance is a(n)
homogeneous mixture
heterogeneous mixture
compound
element

mixtures that appear to be the same throughout are homogenous mixtures

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:

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

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