Which sentence has an agreement error triggered by a two-part noun in an 'a pair of' construction?
The tailor is sharpening a cutting tool.
Both assistants are sorting the fabric rolls.
One damaged button was lying near the door.
A pair of scissors are missing from the drawer.✓Respuesta correcta
Explicación
A pair of scissors has the singular head pair, so its verb must be 'is missing' rather than 'are missing'. The other sentences correctly pair ordinary singular and plural subjects with matching finite verbs.