Under Sunni Muslim law, which of the following is not a ground of irregular (fasid) marriage ?

Under Sunni (Hanafi) Muslim law, a woman having more than one husband at the same time ('Polyandry') renders the second marriage absolutely void (batil), not merely irregular (fasid). By contrast, marriage without required witnesses, marriage with a fifth wife while four wives are living, and unlawful conjunction (marrying two women related within prohibited degrees of conjunction) are treated as irregular (fasid) marriages whose impediment can be removed.