Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and stomach acid. Also, the normal flow of urine washes out microorganisms that enter the urinary tract. The immune system uses white blood cells and antibodies to identify and eliminate organisms that get through the body's natural barriers.
When river water<span> meets </span>sea water<span>, the lighter </span>fresh water<span> rises up and over the denser </span>salt water<span>. </span>Sea water<span> noses into the estuary beneath the outflowing </span>river water<span>, pushing its way upstream along the bottom. Often, as in the Fraser </span>River<span>, this occurs at an abrupt </span>salt<span> front</span>
Answer:
Dark energy
Explanation:
A mysterious force that repels gravity
It's called an erpidermis
