Bad Qubits — Learn Quantum by Doing

Multiple choice

To build the oracle U_f for the balanced function f(x0,x1) = x0 XOR x1 on qubits 0,1 (inputs) and qubit 2 (ancilla), which gates write the function value into the ancilla?

cx(0,2) then cx(1,2)
A single Hadamard on qubit 2
cx(2,0) then cx(2,1)
cx(0,1) then cx(1,0)