我得到了回答这个问题：

i got answer for this question:

enrollmentService.ts

getItems() {

  return this._http.get('static/components/HR/employee_enrollment_form/json/nationality.json')
        .map((responseData) => {
            return responseData.json();
         });

}

Enrollment.ts

constructor(@Inject(EnrollmentService) enrollmentService:EnrollmentService) {

        enrollmentService.getItems().subscribe(res => this.nationality = res);;
}