Which is the best hypothesis for the extinction of the dinosaurs at the end of the Cretaceous period? A.
Mammals evolved and killed the dinosaurs.

B.
Humans destroyed all the dinosaurs.

C.
The climate changed and the dinosaurs could not adapt.

D.
The dinosaurs killed each other.

1. which of the following levels of protein organization shows the complete 3-d arrangement of the polypeptide chain? a) primary b) secondary c) tertiary d) quaternary 2. the carboxyl groups on a protein molecule are composed of which of the following elements? a) nitrogen and hydrogen b) carbon, hydrogen, and oxygen c) carbon and hydrogen d) nitrogen, oxygen, and carbon 3. what part of the protein molecule makes it unique from other proteins? a) the carboxyl group b) the amino group c) the peptide group d) the r group 4. which of the following is an example of a protein that plays a direct role in immune function? a) collagen b) antibodies c) enzymes d) hormones 5. which of the following statements correctly describes the composition of proteins? a) most are composed of 20 common amino acids. b) most are composed of 10 common amino acids. c) most are composed of 20 common fatty acids. d) most are composed of 10 common fatty acids.