Bad Qubits — Learn Quantum by Doing

Multiple choice

On a surface-code patch, the logical operators Xbar and Zbar are strings stretching between opposite boundaries. The lesson explains they anticommute (Xbar Zbar = -Zbar Xbar), exactly like single-qubit X and Z. What geometric fact makes them anticommute?

They overlap on exactly two data qubits, doubling the anticommutation
Their two crossing strings overlap on exactly one data qubit, where X and Z anticommute once
Each string wraps fully around the patch, forming a closed loop
They share no qubits at all, and disjoint operators always anticommute