Answer
A
Work Step by Step
Controlled studies are essential in signifying a difference between the starting study and the modified study.
Environmental Science for AP* (2nd Edition)
by Friedland, Andrew J.; Relyea, Rick
Published by
W. H. Freeman
ISBN 10:
1464108684
ISBN 13:
978-1-46410-868-6
Unit 1 - AP Environmental Science Practice Exam - Section 1: Multiple-Choice Questions - Page 61: 8
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