How to make a query sequence in Angular?

Question

Angular

ngOnInit() {
        this.addressesService.getRegions().subscribe((resp) => {
            this.regions = resp.data.items;
            this.loading = true;
        }, (error) => {
            console.log(error);
        });

        this.addressesService.getObj().subscribe((resp) => {
            this.district = resp.data;
        }, (error) => {
            console.log(error);
        });
// other code
}

How to make a sequence of requests, you need to make it so that only when the first request is executed, run the second one. How to do it using RxJs?