響應式圖片:

<img src="...." class="img-responsive">

響應式16:9影片:

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<div class="embed-responsive embed-responsive-16by9">
  <iframe class="embed-responsive-item" src="https://www.youtube.com/embed/-PcjJOa0p-Q&t=188s"></iframe>
</div>

響應式4:3影片:

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<div class="embed-responsive embed-responsive-4by3">
  <iframe class="embed-responsive-item" src="https://www.youtube.com/embed/-PcjJOa0p-Q&t=188s"></iframe>
</div>