Why do many different types of proteins exist even though there are a limited number of amino acids

"it built up in the atmosphere"

i think thats it, idk, i tried looking for this exact q& a for grad. and idk if i got this question right or sorry if im wrong

1) a

2)c

3)a

4)c

5)b

hope this , if so, your appreciation would be signified through giving   me brainliest, and a you : ) have any further questions? feel   free to ask me in the questions box.