When Is a Proportional Hazard Model (Cox) Used

When is a proportional hazard model (Cox) used?

A) When we wish to graph the survival function of our single event data
B) When we wish to investigate the effect of multiple covariates on the time for a certain event to take place
C) When we wish to test both time-invariant and time-varying covariates
D) When we wish to produce the cumulative survivor function