In most simple type of canal system of porifera, water flows through which one of the following ways
A. Ostia `to` Spongocoel `to` Osculum `to` Exterior
B. Spongocoel `to` Ostia `to` Osculum `to` Exterior
C. Osculum `to` Spongocoel `to` Exterior
D. Osculum `to` Ostia `to` Spongocoel `to` Exterior