Of unknown and unadmitted authorship
A). Gullible
B). Anonymous
C). Unanimous
D). Vexation
Anonymous
One word substitute is Anonymous.
Gullible: easily persuaded to believe something; credulous.
Anonymous: (of a person) not identified by name; of unknown name.
Unanimous: (of two or more people) fully in agreement.
Vexation: the state of being annoyed, frustrated, or worried.