mistake in test???

[Lena Mina]

Hi!
My name is Lena.
Please help with some details in test.
Test (study.ru) "pre- intermediate or intermediate?"
Question №1.
 Have you written down__________ names?

The answers:
a. everybody
b. everybody's
c. everybodys'
d. everybodies'

I marked the answer "с" but the system inform that correct answer - "b".
As I know apostrophe _'_ to write with plural and have following form   _'  (and with singular form _'S).
Why the correct answer "B"?

Best regards,
Lena

[Gibsonmpgu]

everybody - sing

[slavyan]

everybody is a singular pronoun. Your test is ok)

Also the following pronouns are singular either:

•Any
•Anyone (or anybody)
•Anything
•Each
•Everyone (or everybody)
•Everything
•No one
•Nobody
•None
•Nothing
•Some
•Someone (or somebody)
•Something