Which of the following reactions proceeds via a radical intermediate?

• A
  $CH_3-CH=CH_2+HBr \to CH_3-CH(Br)-CH_3$
• B
  $CH_3-CHO+HCN \to CH_3-CH(OH)CN$
• C
  $CH_3-CH=CH_2+HBr \xrightarrow{\text{peroxide}} CH_3-CH_2-CH_2-Br$
• D
  $CH_3CHO+NH_2OH \xrightarrow{H^+} CH_3-CH=N-OH+H_2O$