Which of the following statements is false?

Which of the following statements is false?
  a. The tissues of arthropods are bathed with hemolymph, which delivers oxygen to their
  cells.
  b. In an open circulatory system the heart is still responsible for pumping oxygen-rich fluid.
  c. Earthworms have a central heart that pumps blood to all their tissues.
  d. Blood vessels are found in the open circulatory systems common to some invertebrates.
  e. Hemocyanin is the oxygen transport pigment found in the open circulatory system of
  invertebrates

Question 2

Why doesn't a flatworm have a circulatory system?
  a. The animal is thin enough to permit effective gas exchange by diffusion.
  b. There is not enough room for a circulatory system because of the large gastrovascular
  cavity.
  c. The animal lacks muscles, so it could not have a heart to pump blood.
  d. Only bilaterally symmetrical animals need a circulatory system.
  e. Only vertebrates have circulatory systems.