Estou tentando trabalhar com acessibilidade no meu projeto. Eu adicionei arquivos Reachability.he Reachability.m. Mas depois de construir o projeto xCode me mostra erros estranhos:

Undefined symbols for architecture i386:
"_SCNetworkReachabilityCreateWithName", referenced from:
  +[Reachability reachabilityWithHostname:] in Reachability.o
"_SCNetworkReachabilityCreateWithAddress", referenced from:
  +[Reachability reachabilityWithAddress:] in Reachability.o
"_SCNetworkReachabilitySetCallback", referenced from:
  -[Reachability startNotifier] in Reachability.o
  -[Reachability stopNotifier] in Reachability.o
"_SCError", referenced from:
  -[Reachability startNotifier] in Reachability.o
"_SCErrorString", referenced from:
  -[Reachability startNotifier] in Reachability.o
"_SCNetworkReachabilitySetDispatchQueue", referenced from:
  -[Reachability startNotifier] in Reachability.o
  -[Reachability stopNotifier] in Reachability.o
"_SCNetworkReachabilityGetFlags", referenced from:
  -[Reachability isReachable] in Reachability.o
  -[Reachability isReachableViaWWAN] in Reachability.o
  -[Reachability isReachableViaWiFi] in Reachability.o
  -[Reachability connectionRequired] in Reachability.o
  -[Reachability isConnectionOnDemand] in Reachability.o
  -[Reachability isInterventionRequired] in Reachability.o
  -[Reachability reachabilityFlags] in Reachability.o

Como posso resolver este problema?