Input (grade 13): If the Chelsea-Hackney line were to be built then it would relieve a lot of congestion on the Victoria line, offering an alternative route across Central London between Victoria and King's Cross St. Pancras.
Output (grade 9): If the Chelsea-Hackney line is built then it will relieve a lot of congestion on the Victoria line. It will offer an alternative route across Central London between Victoria and King's Cross St. Pancras.