Answer:
WATER
Step-by-step explanation:
The options attached to this question are given below:
A. Mud.
B. Water.
C. Blood.
D. Air.
Generally, simple invertebrate organisms have simple body structures, which allow exchange of gases to occur through the process of diffusion. Diffusion is a process by which substances are transported from the region of higher concentration to the region of lower concentration. Most simple invertebrates lives in water and they obtain the oxygen they need for survival through the process of diffusion; the oxygen gas diffuse into their body system and the carbon dioxide is also eliminated through the same process.