Match the Research Examples in 1-7 with the Main Threat

Match the research examples in 1-7 with the main threat to internal validity that it contains (a-g) .
-A control and experimental group take a posttest on cultural diversity. The experimental group had a three-day unit on diversity, the control group did not. However, in another class the control group had some discussion about diversity.

A) Maturation
B) History or environmental events
C) Repeated testing
D) Instrumentation
E) Selection or assignment
F) Mortality or attrition
G) Statistical regression