The following statements are related to excretion in invertebrates:

P. Flame cells are found in molluscs and jelly fish.

Q. Nephridia and Malpighian tubules convert ammonia to urea for water conservation.

R. Green glands are found in flatworms and help in the excreta elimination.

S. Excretory canals in nematodes carry waste materials to excretory pores in the body wall.

Choose the correct answer: