如何在angular 2 material设计中的md-select元件上设置默认值？

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

@Component({
  selector: 'app-your-component',
  templateUrl: './your-component.component.html',
  styleUrls: ['./your-component.component.css']
})
export class YourComponent {
  selectedValue = 'option1';
}

<md-select placeholder="Select an option" [(ngModel)]="selectedValue">
  <md-option value="option1">Option 1</md-option>
  <md-option value="option2">Option 2</md-option>
  <md-option value="option3">Option 3</md-option>
</md-select>