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Answer:
B. the long beak helps the bird eat insects.
The proteins(particularly enzymes) of the membrane help chemical reactions.
An example would be enzymes involved in electron transport chain.
Both of these mainly mark or represent markers or identifies within the cell membrane. They are used to identify between different cells of the same type. Also can be used for signalling processes.
That'll be guanine. If you look up "pyrimidine" in google, it will tell you the two nucleotides that are pyrmidines are cytosine and thymine. So that leaves guanine.
