well, there are 32 timeslots,
but you need to carry some signalling channels.
So answers A, B, C are possible (those *may* be possible configurations).
Did you have any dimensioning guidelines in your course ?
For 4 TRX, the usual strategy is to put 1 BCCH ts + 2 SDCCH ts, that leaves 29 TCH. That is the best answer. But A, B, C *may* be possible…