$A$ plant with well-washed roots was placed in a beaker of water diluted with red ink. The red colour travelled up the stem and into the leaf veins. Which of the following is the explanation for the uptake of red ink into the roots?

• A
  The red ink entered the root hairs by osmosis.
• B
  The molecules of red ink diffuse into the root hairs.
• C
  The membranes of the root hairs were destroyed and red ink could enter.
• D
  The molecules of red ink passed from a region of low concentration to one of high concentration.