  The pre-CME structure is of great importance to understanding the origin of
CMEs, which, however, has been largely unknown for CMEs originating from active
regions. In this paper, selected for studying are 16 active-region coronal
arcades whose gradual inflation lead up to CMEs. 12 of them clearly build upon
post-eruptive arcades resulting from a preceding eruption. The observed
inflation sustains for 8.7 +/- 4.1 h, with the arcade rising from 1.15 +/- 0.06
Rsun to 1.36 +/- 0.07 Rsun within the EIT field of view (FOV). The rising speed
is less than 5 km s-1 for most of the time. Only at the end of this
quasi-static stage, it increases to tens of kilometers per second over tens of
minutes. The arcade then erupts out of the EIT FOV as a CME with similar
morphology. This pre-CME structure is apparently unaffected by the flares
occurring during its quasi-static inflation phase, but is closely coupled with
the flare occurring during its acceleration phase. For four events that were
observed on the disk, it is found that the gradual inflation of the arcade is
accompanied by significant helicity injection from photosphere. In particular,
a swirling structure, which is reminiscent of a magnetic flux rope, was
observed in one of the arcades over 4 h prior to the subsequent CME, and the
growth of the arcade is associated with the injection of helicity of opposite
sense into the active region via flux emergence. We propose a four-phase
evolution paradigm for the observed CMEs, i.e., a quasi-static inflation phase
which corresponds to the buildup of magnetic free energy in the corona,
followed by the frequently observed three-phase paradigm, including an initial
phase, an acceleration phase and a gradual phase.
