Planarians lack dedicated respiratory and circulatory systems ...

[Charlie]

Planarians lack dedicated respiratory and circulatory systems because
A) none of their cells are far removed from the gastrovascular cavity or from the external environment.
B) they lack mesoderm as embryos and, therefore, lack the adult tissues derived from mesoderm.
C) their flame bulbs can carry out respiratory and circulatory functions.
D) their body cavity, a pseudocoelom, carries out these functions.

[camila]

Answer has to be A, trust me!

[Charlie]

Wonderful, you were right, thank you so much.