Which of the Following Statements About Ramachandran Plots Is True $\phi$

Multiple Choice

Which of the following statements about Ramachandran plots is true?

A) They are good predictors of protein tertiary structure.
B) They are needed to determine the secondary structure of a protein.
C) They show equal distributions of $\phi$ and $\Psi$ angles for $\alpha$ -helical and $\beta$ -sheet containing proteins.
D) They show that $\beta$ -sheets and $\alpha$ -helices occupy different $\phi$ and $\Psi$ angles.