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Add this:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/web3@1.3.3/dist/web3.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@truffle/contract@4.3.5/dist/truffle-contract.js"></script>