Can someone me with this question?

For #1 im not sure but the amino acids are held together with peptide bonds. For #2 The primary structure of a protein is when the amino acids are in a chain bonded with peptide bonds. This is just a string of amino acids which will then form into a sheet and combine to form a full protein

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?