Angular依赖注入的一个常见错误NullInjectorError,No provider for XXX

export abstract class GreetingService {
    abstract greet(name: string): string;
 }

import { Injectable } from '@angular/core';
import { GreetingService } from './greeting.service';
@Injectable({ providedIn: 'root'})
export class EnglishGreetingService extends GreetingService {
   greet(name: string): string {
      return 'Hello ' + name;
   constructor(){
      super();
      console.log('English class created!');
}

core.js:6241 ERROR NullInjectorError: R3InjectorError(AppModule)[GreetingService -> GreetingService -> GreetingService]: 
  NullInjectorError: No provider for GreetingService!
    at NullInjector.get (http://localhost:4201/vendor.js:8310:27)
    at R3Injector.get (http://localhost:4201/vendor.js:22317:33)
    at R3Injector.get (http://localhost:4201/vendor.js:22317:33)
    at R3Injector.get (http://localhost:4201/vendor.js:22317:33)
    at NgModuleRef$1.get (http://localhost:4201/vendor.js:39618:33)