<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _render_corpus_row(self, label, ngrams):
 """Returns the HTML for a corpus row."""

        row = ('<tr>\n<td>{label}</td>\n<td>{first}</td>\n<td>{only}</td>\n'
               '<td>{last}</td>\n</tr>')
        cell_data = {'label': label}
        for period in ('first', 'only', 'last'):
            cell_data[period] = ', '.join(ngrams[label][period])
        return row.format(**cell_data)