Answer:
Gases like carbon dioxide and oxygen move across the cell membrane using diffusion (option d).
Step-by-step explanation:
The cell membrane is a semi-permeable barrier to the passage of substances through it, having several transport mechanisms to allow the passage of substances.
One of the transmembrane transport mechanisms is simple diffusion, by which gases from respiration —oxygen and carbon dioxide— can pass, as well as small nonpolar molecules.
Simple diffusion is a mechanism that does not require energy, but depends on a transmembrane concentration gradient.
The other options are not correct because they involve transmembrane transport mechanisms that are not used by oxygen and carbon dioxide.