To evaluate a government training program that provides low-income, low-skilled, disadvantaged persons job-specific training, members of the target population are randomly assigned to either a treatment group that is eligible to receive services under the program or to a comparison group that is not. Data are collected on the earnings, welfare receipts, and so forth of both groups during the training period and for three years thereafter. Decide which type of research design it is advised to use.

A. O1XO2, R: O3 O4

B. R: XO2, or R: O4

C. O1XO2

D. R: O1XO2, R: O3 O4