Many people can not learn any lessons from the mistakes______they get hurt somehow.

1. A.
   whether
2. B.
   unless
3. C.
   if
4. D.
   when

Many people can not learn any lessons from the mistakes____they get hurt somehow.?   A.whether             B.unless         C.if                       D.when?

Many people can not learn any lessons from the mistakes 　　　　 they get hurt somehow.