Angular 财产'；forkJoin'；不存在于类型'；可观察的类型'；

我使用的是导入forkJoin的旧语法，我仍然会遇到这个丑陋的错误

它为什么抱怨

 import { Injectable } from '@angular/core';
    import { HttpClient } from '@angular/common/http';
    import { Observable } from 'rxjs/Observable';
    import 'rxjs/observable/forkJoin';
    import 'rxjs/add/operator/map';

    @Injectable()
    export class DataService {

      apiUrl1: string = 'http://localhost:3000/person/?';
      apiUrl2: string = 'http://localhost:3000/facility/?';
      apiUrl3: string = 'http://localhost:3000/exposure/?';

      constructor(private http: HttpClient) { }

      getData(arg): Observable<any> {
        return this.http.get(this.apiUrl1 + arg.data)
            .flatMap((person: any) => Observable.forkJoin(this.http.get(this.apiUrl2 + person.val1), this.http.get(this.apiUrl3 + person.val2)))
            .map(([facility, exposure]) => exposure.val5 * facility.val3)
    }
    }

从'@angular/core'导入{Injectable}；
从'@angular/common/http'导入{HttpClient}；
从“rxjs/Observable”导入{Observable}；
导入“rxjs/observable/forkJoin”；
导入'rxjs/add/operator/map'；
@可注射（）
导出类数据服务{
apirl1:string=http://localhost:3000/person/?';
APIRL2:string=http://localhost:3000/facility/?';
APIRL3:string=http://localhost:3000/exposure/?';
构造函数（私有http:HttpClient）{}
getData（arg）：可观察{
返回this.http.get（this.apirl1+arg.data）
.flatMap（（person:any）=>Observable.forkJoin（this.http.get（this.apirl2+person.val1）、this.http.get（this.apirl3+person.val2）））
.map（（[facility，exposure]）=>exposure.val5*facility.val3）
}
}
正确的导入是
导入'rxjs/add/observable/forkJoin'。注意
add