= Solution
\b[In ordinary perturbative <Standard Model> reactions all three interactions conserve <electric charge>, <four-momentum>, total <angular momentum>, <baryon number>, and total <lepton number>.] The last two are accidental conservation laws of these perturbative processes, not exact nonperturbative statements: <electroweak sphalerons> violate $B+L$ while preserving <baryon-minus-lepton number>. Total <color charge> is respected throughout.
The <strong interaction> and <electromagnetic interaction> also conserve each <net quark flavor number>, including <strangeness>, <charm (quantum number)> and bottom flavour. The <weak charged current> can change them through the <Cabibbo-Kobayashi-Maskawa matrix>. <Isospin> is an approximate <strong interaction> symmetry in the small light-<quark> <mass> difference limit; the different <electric charges> of $u$ and $d$ break it in the <electromagnetic interaction>. Approximate <flavor symmetry> is distinct from exact net-flavour-number conservation by those interactions.
<Parity conservation> and <charge conjugation symmetry> hold for the <electromagnetic interaction> and, assuming a negligible strong CP parameter, the <strong interaction>. The <weak interaction> violates both, and also violates <CP symmetry> in suitable processes. <CPT symmetry> holds under the usual local <Lorentz invariant> <quantum field theory> assumptions. Individual <lepton> family numbers are conserved in the conventional massless-<neutrino> approximation but not in <neutrino oscillations>; an assertion of exact family conservation in all observed reactions would therefore be false.
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