Hello !
So :
1. Travail because in the plural it’s " Travaux " and the others words it’s with a " s " at the end
2. Chacal because in the plural it’s " Chacals " others words are in " aux "
3. Un feu
4. choux ( in the plural it’s with "x" so " des choux " )
5. Un général , because in the plural it’s " des généraux " whereas other has a " s"
6.un vitrail because it’s " des vitraux "
Soo more simple :
1. Travail
2.Chacal
3.Un feu
4.Chou
5.Un général
6.Un vitrail
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Hope i help you ! Bye !