<span>The answer is a certain required chemicals must be actively
transported. Blood brain barrier is a
selective membrane that separates blood circulating from the brain and the
fluid of extracellular in the central nervous system. This is also called a
filtering mechanism, the capillaries that carry blood to the brain and spinal
cord tissue blocking the path way of the certain substance.</span>
I believe it’s the first, third and fourth ones. I might be wrong and I’m sorry if I am.
Answer:
One of the physical characteristics about a gas is that it is not a solid and it is an invisible gas
Explanation:
12. One of the physical characteristics about a gas
Tree grass, bug's like ants wasp bees ,flowers,and weeds stuff like that
