Which of the Following Statements Is True About the Cohort-Sequential

Which of the following statements is true about the cohort-sequential design?

A) In this design, the naturally occurring event is a quasi-independent variable.
B) In this design, one includes a time series component along with a control group that is not exposed to any treatment.
C) This design is a variation on the basic time series design, and it charts changes in behavior as a function of some naturally occurring event.
D) This design lets one evaluate the degree of contribution made by factors such as generation effects.