使用引导程序时我无法打开汉堡包菜单。有人能告诉我代码有什么问题吗？
我直接从引导程序网站上提取了代码。我看过其他人关于这个问题的问题，但建议的解决方案没有帮助。
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<nav class="navbar fixed-top navbar-expand-lg navbar-light" style="background-color: #ffffff;">
<a class="navbar-brand" href="index.html">
<img src="logo.png" width="200" height="200" class="d-inline-block align-top" alt="">
</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarNav">
<ul class="navbar-nav">
<li class="nav-item active">
<a class="nav-link" href="index.html">Home <span class="sr-only">
(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="portfolio.html">Portfolio </a>
</li>
<li class="nav-item">
<a class="nav-link" href="about.html">About </a>
</li>
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<a class="nav-link" href="contact.html">Contact </a>
</li>
</ul>
</div>
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