Answer: A. They all exchange gases with the environment.
Step-by-step explanation:
The plants, humans and flatworm are the complex eukaryotic organisms which performs a vital function of respiration. In respiration the carbon dioxide gas is expelled out of the body whereas the oxygen is taken inside the body. In plants the exchange of gases takes place through tiny pores called as stomata. In humans the exchange of gas occurs through complex organs like skin, and nose. In flatworm the exchange of gases takes place through the tiny pores present on the outer membrane of the body.