Which statement about osmosis is not true?
$a .$ It obeys the laws of diffusion.
$b$. In animal tissues, water moves into cells if they are hypertonic to their environment.
$c .$ Red blood cells must be kept in a plasma that is hypotonic to the cells.
d. Two cells with identical solute concentrations are isotonic to each other.
e. Solute concentration is the principal factor in osmosis.