Question

Which sentence does not contain any errors?

A.
She couldnt have known that the box was theirs.

B.
She couldn't have known that the box was theirs.

C.
She couldn't have known that the box was their's.

D.
She could'nt have known that the box was theirs'.

Answer 1

it's between b and c

Answer 2

you're right.
"their's" is not a word, though (it would be there's, but if that was the case then that word would not belong in the sentence, and it would be wrong, anyway), so what do you think?

Answer 3

b

Answer 4

yes (: