The answer is A . C can`t be 0 so option(c) is canceled and if you put option (b) values then Y= 0 (i think 'f' is Y here ). So (b) is canceled . Remaining A and D both satisfied the circuit (Y =1 ) but if you see they say the "STEADY state" , so before turning on the circuit the value of Y (f) may be 0 , now
option (d) then A(1) nand 0(f) = 1 ------> B(1) nand 1 = 0 -----> C(1) and 0 = 0 (f)
option (a) then A(0) nand 0(f) = 1 ------> B(0) nand 1 = 1 -----> C(1) and 1 = 1 (f) satisfied the circuit .