Dr. $F$. Went noted that if coleoptile tips were removed and placed on agar for one hour,the agar would produce a bending when placed on one side of freshly-cut coleoptile stumps. Of what significance is this experiment?

• A
  It made possible the isolation and exact identification of auxin.
• B
  It is the basis for quantitative determination of small amounts of growth-promoting substances.
• C
  It supports the hypothesis that $IAA$ is auxin.
• D
  It demonstrated polar movement of auxins.