B must be the answer.
Irrecoverability is when a committed transaction has to be rolled back .
A cannot be the answer , since T2 is writing A irrespective of the changes made by T1(This is called Blind Write).
B has to be the answer , since T2 is reading what T1 wrote and T1 is not committed till now . So there's a potential chance that T2 would be needed to rollback if T1 failed , to maintain consistency.
C cannot be answer since transaction is committed and D cannot be answer since Read Read are not conflicting opertations