:left;"> controlling-column-types-5 </td>
   <td style="text-align:left;"> exercise </td>
   <td style="text-align:left;"> df = read_csv(simple_csv, col_types = list(x = col_double()))
problems(df) </td>
  </tr>
  <tr>
   <td style="text-align:left;"> controlling-column-types-6 </td>
   <td style="text-align:left;"> exercise </td>
   <td style="text-align:left;"> read_csv(simple_csv, na = ".") </td>
  </tr>
  <tr>
   <td style="text-align:left;"> controlling-column-types-7 </td>
   <td style="te