GMAT Sentence Correction (SC) | Re: Only seven people this century have been killed by the great

The Columbia Guide to Standard American English by Kenneth G. Wilson, lists the following under the entry "Indefinite pronoun":

"Anyone, anybody, someone, somebody, none, each, either, neither, one...."

All of these take an apostrophe when forming the possessive. I can be confident of this because (1) none of them has a possessive form written simply with a terminal s as an entry in the Oxford English Dictionary--and if any dictionary would list such forms it is the OED--and