= Solution
Measured half-integer <spin> and fermionic behavior rule out a simple <quark>-<antiquark> pair: two spin-$1/2$ constituents have integer total <spin>, and adding integer <orbital angular momentum> does not change that. Their measured <baryon number> $B=1$, inferred through production and conservation bookkeeping, corresponds to $n_q-n_{\bar q}=3$. Their pattern of <electric charges>, <strangeness> and <isospin> then agrees with three light <valence quarks>.
<Baryon magnetic moments> provide a more detailed check. The additive <quark model> gives, for example,
$$
\mu_p=\frac43\mu_u-\frac13\mu_d,\qquad
\mu_n=\frac43\mu_d-\frac13\mu_u.
$$
Approximately equal up and down constituent <masses> give $\mu_u\simeq-2\mu_d$, hence $\mu_p/\mu_n\simeq-3/2$, close to the measured ratio of about $-1.46$.
These observations support three \b[valence] <quarks>; they do not prove the absence of extra <quark>-<antiquark> pairs. For instance, $qqqq\bar q$ also has $B=1$ and can have half-integer <spin>. Ordinary <Quantum chromodynamics> <baryons> also contain sea pairs and <gluons>. The stronger interpretation that the measurements exclude every <antiquark> component is therefore false.
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