In Which of the Following Cases Would You Want to Use

Multiple Choice

In which of the following cases would you want to use difference-in-difference estimation?

A) When individuals non-randomly select different outcomes of the dependent variable.
B) When you are attempting to replicate a randomized clinical trial.
C) When you are dealing with non-negative count data.
D) When you suspect that the marginal effects are different for different values of the dependent variable.