Upper one is an XOR gate and lower one is XNOR gate, we know that XOR and XNOR are compliments of each other, hence for same inputs A and B, one of these gate will give 0 and other gate will give 1 (The values of A and B won’t matter here). …………...(i)
Now, the gate in the right side is again an XNOR gate, consider it as NOT of XOR, it would be easier to analyze.
Now, we want the NOT of XOR to be 1, hence the result of XOR has to 0.
We already know that among the upper 2 inputs, one input is 1 and other is 0 (from what we observed in (i)).
Also, 1 XOR 0 = 1, hence upper 2 lines will result in 1.
Now you want to make 1 XOR C = 0, which is possible only if C is 1.
Hence, option 4 is correct.