Answer:
water, carbon monoxide gas, Small lipid soluble substances
Step-by-step explanation:
The BBB is a highly selective semi permeable membrane which prevents the solute in the blood from crossing or passing through the central nervous system of human brain.
It separates the blood from the brain.
In the context,
-- Water successfully crosses the BBB without any help. It can cross through diffusion.
-- carbon monoxide gas can cross BBB. Haemoglobin in blood has 200 times more affinity towards the carbon monoxide when it is compared with oxygen. This is why carbon monoxide poisoning affects the brain.
--- Small lipid soluble substances can also cross BBB without any help.