DrLaGuardia Is Curious as to Whether Children in a Daycare

Dr.LaGuardia is curious as to whether children in a daycare center will share more after watching an education video on sharing.Immediately before and after the video,he has several undergraduate research assistants code the sharing behavior of a group of 33 four-year-olds.Which of the following would you recommend to her to decrease the threat of instrumentation?

A) Establishing the reliability and validity of her coders at pretest
B) Establishing the reliability and validity of her coders at posttest
C) Using clear coding manuals
D) All of the above should be recommended
E) None of the above should be recommended