I think its C.
I hope this helps and please do correct me if im wrong.
The types of unconformities that can occur in rock layers are: ANGULAR, NONCONFORMITY and DISCONFORMITY.
Answer:
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She could use a control to compare her data to and make sure it is cleaner. Ex. Use the old detergent on ten shirts and then use the new detergent on another ten shirts. She would then compare the shirts she did each detergent on and come up with her conclusion.
