= Solution
For $q=(u,d)^T$, massless two-flavour <Quantum chromodynamics> has
$$
\mathcal L=-\frac12\operatorname{tr}(G_{\mu\nu}G^{\mu\nu})
+i\bar q\not Dq.
$$
Classically its continuous global symmetry is $SU(2)_L\times SU(2)_R\times U(1)_V\times U(1)_A$, up to finite central quotients. The <Adler-Bell-Jackiw anomaly> destroys the continuous axial $U(1)_A$ in the quantum theory, leaving $SU(2)_L\times SU(2)_R\times U(1)_V$, together with an anomaly-preserved discrete axial subgroup.
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