显示下拉框中的所选项目，并以表格格式显示它们

<select id="dropdown" onchange="displaySelected()">
  <option value="project1">项目1</option>
  <option value="project2">项目2</option>
  <option value="project3">项目3</option>
</select>

<table id="table">
  <thead>
    <tr>
      <th>项目名称</th>
      <th>项目描述</th>
    </tr>
  </thead>
  <tbody id="tableBody">
  </tbody>
</table>

function displaySelected() {
  var dropdown = document.getElementById("dropdown");
  var selectedValue = dropdown.value;
  var tableBody = document.getElementById("tableBody");
  
  // 清空表格内容
  tableBody.innerHTML = "";
  
  // 根据所选项目添加行
  if (selectedValue === "project1") {
    addTableRow("项目1", "这是项目1的描述");
  } else if (selectedValue === "project2") {
    addTableRow("项目2", "这是项目2的描述");
  } else if (selectedValue === "project3") {
    addTableRow("项目3", "这是项目3的描述");
  }
}

function addTableRow(name, description) {
  var tableRow = document.createElement("tr");
  
  var nameCell = document.createElement("td");
  nameCell.textContent = name;
  tableRow.appendChild(nameCell);
  
  var descriptionCell = document.createElement("td");
  descriptionCell.textContent = description;
  tableRow.appendChild(descriptionCell);
  
  var tableBody = document.getElementById("tableBody");
  tableBody.appendChild(tableRow);
}