The Main Difference Between Protonephridia and Metanephridia Is That

The main difference between protonephridia and metanephridia is that:

A) protonephridia are involved in osmoregulation, while metanephridia are involved in excretion.
B) protonephridia consist of blind flame cells, while metanephridia consist of tubules open at both ends.
C) protonephridia are involved in excretion, while metanephridia are involved in osmoregulation.
D) protonephridia consist of tubules open at both ends, while metanephridia consist of blind flame cells.
E) protonephridia are found in annelids and metanephridia are found in flatworms.