Answer:
d
Explanation:
In a randomized, controlled, double-blind study neither the experimenter nor the subject know whether the subject is in a control group or an experimental group.
Randomized double-blind placebo control (RDBPC) trials are considered the epidemiological research of "gold standard." The best analogy is placebo management, which requires blindness of subjects, researchers and test workers. Trial's advantage over an observational study is its the ability to convey causality.
B. rabbits changing fur color
Other organism would have to compete with the Zebra Mussels and most likely cause a collapse within these different populations
Because it causes them to move, and so they weather that way. Buut the acid rain can leak into the rock and slowly break down the atoms, causing it to chemically weather faster. Also, just regular water/rain can wash away some covering sediment.