  We prove that every usco multimap $\Phi:X\to Y$ from a metrizable separable
space $X$ to a GO-space $Y$ has an $F_\sigma$-measurable selection. On the
other hand, for the split interval $\ddot{\mathbb I}$ and the projection
$P:\ddot{\mathbb I}^2\to{\mathbb I}^2$ of its square onto the unit square
${\mathbb I}^2$, the usco multimap $P^{-1}:{\mathbb I}^2\multimap\ddot{\mathbb
I}^2$ has a Borel ($F_\sigma$-measurable) selection if and only if the
Continuum Hypothesis holds. This CH-example shows that know results on Borel
selections of usco maps into fragmentable compact spaces cannot be extended to
a wider class of compact spaces.
