问角ngclass如何使用多个类和条件

EN

<div
  class="normal"
  [ngClass]="{
    green: selection.nature,
    blue: selection.sky,
    red: selection.love,
    yellow: selection.friendship
  }"
>
  <button (click)="select('nature')">NATURE</button>
  <button (click)="select('sky')">SKY</button>
  <button (click)="select('love')">LOVE</button>
  <button (click)="select('friendship')">FRIENDSHIP</button>
</div>

selection = {
    nature: false,
    sky: false,
    love: false,
    friendship: false,
  };
  select(value: string) {
    Object.keys(this.selection).forEach((k) => (this.selection[k] = false));
    this.selection[value] = true;
  }