mat-select在Angular中不能正常工作

// app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { MatSelectModule } from '@angular/material/select';
import { MatFormFieldModule } from '@angular/material/form-field';
import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    BrowserAnimationsModule,
    MatSelectModule,
    MatFormFieldModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

<!-- app.component.html -->
<mat-form-field>
  <mat-label>Select an option</mat-label>
  <mat-select [(value)]="selectedValue">
    <mat-option *ngFor="let option of options" [value]="option.value">
      {{option.viewValue}}
    </mat-option>
  </mat-select>
</mat-form-field>

// app.component.ts
import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  selectedValue: string;
  options = [
    {value: 'option1', viewValue: 'Option 1'},
    {value: 'option2', viewValue: 'Option 2'},
    {value: 'option3', viewValue: 'Option 3'}
  ];
}