  We perform calculations of our one-dimensional, two-zone disk model to study
the long-term evolution of the circumstellar disk. In particular, we adopt
published photoevaporation prescriptions and examine whether the
photoevaporative loss alone, coupled with a range of initial angular momenta of
the protostellar cloud, can explain the observed decline of the frequency of
optically-thick dusty disks with increasing age. In the parameter space we
explore, disks have accreting and/or non-accreting transitional phases lasting
of $\lesssim20 %$ of their lifetime, which is in reasonable agreement with
observed statistics. Assuming that photoevaporation controls disk clearing, we
find that initial angular momentum distribution of clouds needs to be weighted
in favor of slowly rotating protostellar cloud cores. Again, assuming inner
disk dispersal by photoevaporation, we conjecture that this skewed angular
momentum distribution is a result of fragmentation into binary or multiple
stellar systems in rapidly-rotating cores. Accreting and non-accreting
transitional disks show different evolutionary paths on the $\dot{M}-R_{\rm
wall}$ plane, which possibly explains the different observed properties between
the two populations. However, we further find that scaling the photoevaporation
rates downward by a factor of 10 makes it difficult to clear the disks on the
observed timescales, showing that the precise value of the photoevaporative
loss is crucial to setting the clearing times. While our results apply only to
pure photoevaporative loss (plus disk accretion), there may be implications for
models in which planets clear disks preferentially at radii of order 10 AU.
