Typescript Angular Material 组件不起作用：'matoption' 不是已知元素

我正在try 添加角material 组件.但该组件没有正常工作.这个错误说

Uncaught Error: Template parse errors: 'mat-option' is not a known element:
// ...

我认为错误来自app.module.ts:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { SidebarComponent } from './sidebar/sidebar.component';
import { PostsComponent } from './posts/posts.component';
import { UsersComponent } from './users/users.component';
import { DetailsComponent } from './details/details.component';
import { HttpClientModule } from '@angular/common/http';
import { FooterComponent } from './footer/footer.component'; 
import {MatButtonModule, MatCheckboxModule} from '@angular/material';
import {MatFormFieldModule} from '@angular/material/form-field';
import { MyFormComponent } from './my-form/my-form.component';
@NgModule({
  declarations: [
    AppComponent,
    SidebarComponent,
    PostsComponent,
    UsersComponent,
    DetailsComponent,
    FooterComponent, MyFormComponent
  ],
  imports: [
    BrowserModule, AppRoutingModule,HttpClientModule,MatButtonModule, MatCheckboxModule,MatFormFieldModule
  ]
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }