"Foli a deux" is: (A) Delusion of doubles, (B) Substance abuse disorder, (C) Sharing delusion with one more person, (D) Dissociation disorder
Answer is C. The person with delusion influences the other to develop same delusion.
2 persons sharing same delusion  - "Foli a deux".
3 persons sharing same delusion  - "Foli a trios".
Sharing a delusion to group of people : Pseudo community.