What Is the Disadvantage to Historical Control Designs? Select All

What is the disadvantage to historical control designs? Select all that apply.

A) Historical control designs cannot establish cause and effect.
B) In historical control designs, treatments are limited to only those treatments that will wash out over time.
C) Historical control designs do not assign participants to groups by random assignment.
D) With historical control designs, because the control and treatment groups are not studied at the same time, it is difficult to know whether the two groups are different because of the intervention or the differences in time.