The sentence that uses possessive personal pronouns correctly is A. Have you seen the cat and its kittens?
B. is wrong because (their's) is not a word, it would have to be their or theirs, no apostrophe.
C. Stanley claimed that the papers were his'. is wrong because (his) is the possessive no apostrophe after the s.
D. is wrong because (it's) is a contraction for 'it is'. And you wouldn't say, the squirrel twitched it is tail.
Hope this helps. :)
