Both are correct, actually. It can be a shorter form of "Ciebie", but here it is plural of "ten" = "these".
Fun fact: when writing something directly to another person (a letter/a text message/a facebook message/etc.) it's polite to capitalize all forms of 'you': Ci, Tobie, Twój, etc. It is not done in this course because these are just sentences without any context. But because of that, sometimes some people mistakenly capitalize 'ci' meaning 'these', although it's in fact a different word :D