  In this paper, vacuum and singularity formation are considered for
compressible Euler equations with time-dependent damping. For $1<\gamma\leq 3$,
by constructing some new control functions ingeniously, we obtain the lower
bounds estimates on density for arbitrary classical solutions. Basing on these
lower estimates, we succeed in proving the singular formation theorem for all
$\lambda$, which was open in [1] for some cases.Moreover, the singularity
formation of the compressible Euler equations when $\gamma=3$ is investigated,
too.
