Which of the following is least readily formed by cationic polymerization?

A) poly(acrylonitrile)
B) poly(isobutylene)
C) poly(propylene)
D) polystyrene
E) All of the above have equal propensity to undergo cationic polymerization.

The following structure is a proteasome inhibitor that may find application in treating cervical cancer (J. Med. Chem. 2011, 449) . The halides in this structure may be classified as ________ and ________.

A) vicinal; vinyl
B) vicinal; aryl
C) vinyl; aryl
D) vinyl; geminal