  Using results of nucleosynthesis calculations for theoretical core-collapse
supernova models with various progenitor's masses, it is shown that abundance
patterns of C, Mg, Si, Ca, and H seen in extremely metal-deficient stars with
[Fe/H] < -2.5 follow those seen in the individual first generation supernova
remnants (SNRs). This suggests that most of the stars with [Fe/H] < -2.5 were
made from individual supernova (SN) events. To obtain the ratio of heavy
elements to hydrogen, a formula is derived to estimate the mass of hydrogen
swept up by a SNR when it occurs in the interstellar matter with the primordial
abundances. We use [Mg/H] to indicate the metallicities instead of [Fe/H]. The
metallicities [Mg/H] predicted from these SNRs range from ~-4 to ~-1.5 and the
mass of Mg in a SN is well correlated with its progenitor's mass. Thus the
observed [Mg/H] in an extremely metal deficient star has a correspondence to
the progenitor's mass. A larger [Mg/H] corresponds to a larger progenitor's
mass. Therefore, so called `age-metallicity relation' does not hold for stars
with [Fe/H] < -2.5. In contrast, the [Mg/Fe] ratios in the theoretical SNRs
have a different trend from those in extremely metal-deficient stars. It is
also shown that the observed trend of [Mg/Fe] can predict the Fe yield of each
SN given the correspondence of [Mg/H] to the progenitor's mass. The Fe yields
thus obtained are consistent with those derived from SN light curve analyses.
This indicates that there is still a problem in modelling a core-collapse
supernova at its beginning of explosion or mass cut.
