to return the mock data from Observable in angular service

//to return the mock data from Observable in angular service

//Generic type 'Observer<T>' requires 1 type arguments(s).

getStudentSubjectDropdown(studentID: string): Observable<dropDownData[]> {

    //const params = new HttpParams().append('studentId', studentID);

    //return this.http.get<dropDownData[]>(this.rootURL + 'Student/StudentSubject', { params }).pipe(retry(3));

    let data: dropDownData[] = [

      {

        "id": "1001",

        "name": "Telugu",

        "description": "Telugu is First Language"

      },

      {

        "id": "1002",

        "name": "Hindi",

        "description": "Hindi is Second Language"

      },

      {

        "id": "1003",

        "name": "English",

        "description": "English is Third Language",

      },

      {

        "id": "1004",

        "name": "Mathematics",

        "description": "Maths is a subject"

      },

      {

        "id": "1005",

        "name": "Science",

        "description": "Science is a subject"

      },

      {

        "id": "1006",

        "name": "Social",

        "description": "Social is a subject"

      }

    ],

    return new Observable(( observer: Observer<dropDownData[]>) => {

    observer.next(data);

    observer.complete();

  });

}