I neddd help

It's D

Explanation:

A: Is wrong due to the fact that longer time spans give more credibility

B: Multiple group testing is needed

C: C makes it better because multiple groups would create more diversity than just 2 groups, but this is unnecesary

D: We need a control group

emerald ash borer

the emerald ash borer is a green buprestid or jewel beetle native to north-eastern asia that feeds on ash species. females lay eggs in bark crevices on ash trees, and larvae feed underneath the bark of ash trees to emerge as adults in one to two years. hope this !

just here for the other one bc they put up with u