D i am pretty sure is right
Antibodies have a variable region that binds to a specific antigenic determinant.
Antibody
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. Each tip of the "Y" of an antibody contains a paratope (analogous to a lock) that is specific for one particular epitope (analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system or can neutralize it directly (for example, by blocking a part of a virus that is essential for its invasion).
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Ocean acidification causes a decrease in the pH concentration of the oceans, mostly arises as a result of the entry of carbon dioxide from the atmosphere.
A fisherman noticing a shellfish's shell being very small and lack the thick hard shell may be due to Ocean acidification (option A).
- Ocean acidification is mainly caused by fossil fuels and leads to a decrease in the water's pH.
- It also causes a reduction in the amount of carbonate, a building block of shells and skeletons in seawater.
- This makes it very difficult for marine organisms, such as shell fish and corals, to form their shells and skeletons, and those with existing shells may begin to dissolve.
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