  We present high-angular resolution sub-millimeter continuum images and
molecular line spectra obtained with the SMA toward two massive cores that lie
within Infrared Dark Clouds; one actively star-forming (G034.43+00.24 MM1) and
the other more quiescent (G028.53-00.25 MM1). The high-angular resolution
sub-mm continuum image of G034.43+00.24 MM1 reveals a compact (~0.03 pc) and
massive (~29 Msun) structure while the molecular line spectrum shows emission
from numerous complex molecules. Such a rich molecular line spectrum from a
compact region indicates that G034.43+00.24 MM1 contains a hot molecular core,
an early stage in the formation of a high-mass protostar. Moreover, the
velocity structure of its 13CO(3-2) emission indicates that this B0 protostar
may be surrounded by a rotating circumstellar envelope. In contrast, the sub-mm
continuum image of G028.53-00.25 MM1 reveals three compact (<0.06 pc), massive
(9-21 Msun) condensations but with no lines detected in its spectrum. We
suggest that the core G028.53-00.25 MM1 is in a very early stage in the
high-mass star-formation process; its size and mass are sufficient to form at
least one high-mass star, yet it shows no signs of localized heating. Because
the combination of high velocity line wings with a large IR-mm bolometric
luminosity (~100 Lsun) indicates that this core has already begun to form
accreting protostars, we speculate that the condensations may be in the early
phase of accretion and may eventually become high-mass protostars. We,
therefore, have found the possible existence of two high-mass star-forming
cores; one in a very early phase of star-formation and one in the later hot
core phase. Together the properties of these two cores support the idea that
the earliest stages of high-mass star-formation occur within IRDCs.
