A.{α|-60°≤α≤60°}
B.{α|k·180°-60°≤α≤k·360°+30°,k∈Z}
C.{α|k·360°+30°≤α≤k·360°-60°,k∈Z}
D.{α|k·360°-60°≤α≤k·360°+30°,k∈Z}
D