Who's To Blame? (1) A Wee Thought-Experiment

Consider the following story:
Person A tells a fairly transparent lie to person B.
Person B transmits the lie to a whole group of people, C...M
C...M believe the transparent lie, and freak out.
Person N collects some evidence and shows what should already have been obvious, that the lie is a lie.
Question: Who is to blame here? (Choose all that apply):
(a) Person A
(b) Person B
(c) Persons C...M

[This actually leaves out:
(d) Person O, who has spent the last several years browbeating C...M into believing that they should always believe every accusation no matter how implausible...]