Task: Sentence Expansion
Input (English): In the oxygen- and sulfur-containing aromatic rings , one of the electron pairs of the heteroatoms contributes to the aromatic system ( similar to the non-basic nitrogen-containing rings ) .
Output (English): In the oxygen- and sulfur-containing aromatic rings , one of the electron pairs of the heteroatoms contributes to the aromatic system ( similar to the non-basic nitrogen-containing rings ) , whereas the second lone pair extends in the plane of the ring ( similar to the primary nitrogen-containing rings ) .