For Quasi-Experiments

For quasi-experiments,

A) there is a particularly important potential threat to internal validity, namely whether the "as if" randomization in fact can be treated reliably as true randomization.
B) there are the same threats to internal validity as for true randomized controlled experiments, without modifications.
C) there is little threat to external validity, since the populations are typically already different.
D) OLS estimation should not be used.