Mat Table Angular仅从数组打印最后的数据，该数组也打印每行中的每个字母

import { MatTableModule } from '@angular/material/table';

@NgModule({
  imports: [
    MatTableModule
  ],
  ...
})
export class AppModule { }

<table mat-table [dataSource]="data">
  <ng-container matColumnDef="letters">
    <th mat-header-cell *matHeaderCellDef> Letters </th>
    <td mat-cell *matCellDef="let element"> {{ element }} </td>
  </ng-container>

  <tr mat-header-row *matHeaderRowDef="columns"></tr>
  <tr mat-row *matRowDef="let row; columns: columns;"></tr>
</table>

import { Component } from '@angular/core';

@Component({
  selector: 'app-table',
  templateUrl: './table.component.html',
  styleUrls: ['./table.component.css']
})
export class TableComponent {
  data: string[] = ['A', 'B', 'C', 'D', 'E'];
  columns: string[] = ['letters'];
}