  The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in
characterising the formation and evolution of the first stars and the Galaxy
since the extremely-poor (EMP) stars with [Fe/H] \leq -2.5 share the common
features of carbon enhancement in their surface chemical compositions. The
origin of these stars is not yet established due to the controversy of the
origin of CEMP stars without the enhancement of s-process element abundances,
i.e., so called CEMP-no stars. In this paper, we elaborate the s-process
nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We
find that the efficiency of the s-process is controlled by O rather than Fe at
[Fe/H] \lesssim -2. We demonstrate that the relative abundances of Sr, Ba, Pb
to C are explained in terms of the wind accretion from AGB stars in binary
systems.
