Solution:
The sentences 1 and 3 do not indicate anything about Chris being related to ballet dancing.
Find the two sentences that together prove;
Chris is a ballet dancer.
1. Chris loves dancing.
2. Chris is in a dance troupe called Bellas.
3. Ballet is a difficult dance forms.
4. Bellas is a group of ballerinas.
The sentences 1 and 3 do not indicate anything about Chris being related to ballet dancing.