Which statement does not describe cell cycle checkpoint

What must be true for natural selection to heppen

Ronald wants to see if a new shower cleaner works better in removing soap than his old cleaner. he uses the new cleaner on one half of the shower tiles and his old cleaner on the other half. identify the independent and dependent variables in this experiment. enter your answer in the space provided.

_tissues respond quickly to outside stimuli a) epithelia b)nervous c)muscular d)muscular and nervous