B. One
because an independent variable is something you change. So in a scientific experiment you only change one thing. If you happen to change more than one thing then the test becomes unfair therefore you should repeat and make sure that only one thing is changed this time.
Answer:
One could be in the cell. The cell respires, thus producing carbon dioxide in it. So the concentration builds up in the cell. Diffusion is the net movement of particles from a region of high concentration to a region of low concentration, and the carbon dioxide concentration outside the cell is less, therefore the carbon dioxide molecules moves outs of the cell.
Another scenario is when perfume is sprayed into the air. The perfume particles collides with the air particles (lower or no concentration of perfume). This process goes on and on. This is diffusion since the concentration perfume particles collides with the less concentrated particles of perfume.
B; An unshelled fish is lively and elusive past the power of words to portray, and in this, undoubtedly, lies its desirability.
It will be better for the population
