Answer:
The answer should be C: mostly in the 20th century
Explanation:
True. A protein becomes functional only when it reaches its tertiary shape (3D). It is not necessary for the protein to reach the quaternary stage, but that is just a more complex functioning protein. It really is just two tertiary merged together. Example is red blood cells.
Answer:
The bottom one shows how the circulatory system of a fish functions.
im pretty sure its adaptation <3