Side chains of amino acids are are:
A. all nonpolar
B. non-polar if they contain N or S
C. all polar
D. may be polar or nonpolar
E. none of the above choices is correct

Side chains which have pure hydrocarbon alkyl groups (alkane branches) or aromatic (benzene rings) are non-polar. Examples include valine, alanine, leucine, isoleucine, phenylalanine. The number of alkyl groups also influences the polarity. The more alkyl groups present, the more non-polar the amino acid will be.