I'm like so sorry that I'm a teacher on this website but please stop cheating.
It relates to the actual meaning which is "<span>a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change."</span>
We brought books,so I hope they will bring
(3.)theirs
its number three because if you stated i hope they will bring their ..... its incomplete
or if you put i hope i bring them ..... its just not sounding right...