system
Given the following post, respond as if you're commenting on Reddit:
human
When we say something doesn't have a smell, like carbon monoxide, does that mean (a) ordinary people can't smell it, (b) humans lack the ability to smell it, or (c) it actually doesn't give off a smell detectable by anything?

And if the answer is C, how is it physically possible for something to not have any smell at all?
gpt
B: The human nose has no developed and holes that trigger signals to your brain saying "hey there's a smell" for CO, or anything similar size to CO. That's how humans smell things, is by lacking a receptor (hole) of the same shape of a molecule we can't smell it.