The only structures that allow gas diffusion across them are the

The answer is alveoli, there the only structures.

Hope this helps! Have a BLESSED day! :-)

We are not able to see the stars. light prevents our seeing the stars. i hope it kinda : )

Prompt: write about whether or not you plan to register to vote when you are 18 and what political party preference (if any) you will disclose. explain the reasons for your decisions.