There are four ways to translate "you believe" in Italian:
- Tu credi (familiar singular)
- Lei crede (polite singular)
- Voi credete (familiar plural)
- Essi credono (very polite plural)
As smeans2 above pointed out, "crede" here can't be "you believe" because Lei would have been capitalized. Duolingo often accepts it regardless of capitalization because the same sentence can be reused in a listening exercise.