A D-Amino Acid Would Interrupt An $\alpha$ Helix Made of L-Amino Acids

Multiple Choice

A D-amino acid would interrupt an $\alpha$ helix made of L-amino acids. Another naturally occurring hindrance to the formation of an $\alpha$ helix is the presence of:

A) a negatively charged Arg residue.
B) a nonpolar residue near the carboxyl terminus.
C) a positively charged Lys residue.
D) a Pro residue.
E) two Ala residues side by side.