Bad Qubits — Learn Quantum by Doing

Multiple choice

On a 3-data-qubit chain with checks S1 = Z0 Z1 and S2 = Z1 Z2, a single bit-flip X strikes the MIDDLE data qubit (qubit 1). What syndrome (S1, S2) do the two checks report, and why?

(1, 0): only S1 reacts because it is listed first
(0, 0): a middle error is invisible because the two checks cancel it
(1, 1): qubit 1 is shared by both checks, so flipping it makes both parities odd
(0, 1): only S2 reacts because qubit 1 is its first operand