private void BindCategory() 
         { 
             string sql = ReportForm.Properties.Settings.Default.CEC710ConnectionString; 
             SqlConnection conn = new SqlConnection(sql); 
  
             DataSet1 myData = new DataSet1(); 
             SqlDataAdapter da = null; 
              
             da = new SqlDataAdapter("select b.name from BuildNumber a inner join Category b on a.BNumber = b.BNumber where a.Description = '" + comboBox1.SelectedValue + "'", conn); 
             da.Fill(myData, "Category"); 
  
             this.comboBox3.DataSource = myData; 
             this.comboBox3.DisplayMember = myData.Tables[0].Columns[2].ColumnName; 
             this.comboBox3.ValueMember = myData.Tables[0].Columns[2].ColumnName; 
         } 
 

            this.comboBox3.DataSource = myDataTables[0];
            this.comboBox3.DisplayMember = myData.Tables[0].Columns[2].ColumnName;
            this.comboBox3.ValueMember = myData.Tables[0].Columns[2].ColumnName;

------解决方案--------------------
        private void BindCategory()
       {
           string sql = ReportForm.Properties.Settings.Default.CEC710ConnectionString;
           SqlConnection conn = new SqlConnection(sql);

           DataSet1 myData = new DataSet1();
           SqlDataAdapter da = null;
          
           da = new SqlDataAdapter("select b.name as CategoryName from BuildNumber a inner join Category b on a.BNumber = b.BNumber where a.Description = '" + comboBox1.SelectedValue + "'", conn);
           da.Fill(myData, "Category");

           this.comboBox3.DataSource = myData;
           this.comboBox3.DisplayMember = myData.Tables[0].Columns[2].ColumnName;
           this.comboBox3.ValueMember = myData.Tables[0].Columns[2].ColumnName;
       }
this.comboBox3.DataSource = myData.Tables[0];
 this.comboBox3.DisplayMember = "CategoryName";
 this.comboBox3.ValueMember = "CategoryName";