Answer:
The correct answer is option D. they were part of the control group.
Explanation:
A control group is a group of subjects different from the other test subject as they did not get the independent variable's effect on them and separated from the rest of the experiment. This group of subjects is used to rule out any other explanation of the effect of the independent variable.
In this experiment, subjects that received a placebo injection are the control group as they did not expose to the mutated virus and there are the presence of antibodies in the blood.
Marine biologists study changes in the ocean. so they will look at the chemical composition of deep waters and see how consecrated the oxygen is. They will also study the movements of the plates because when planted move it usually makes new food for deep life
they will also check animal concentrations in certain areas.
Another thing they do is track animal movements. this could be by putting a tracker on a whale or a shark or anything and watching its depths it goes or watching the distance it goes in a day.
Answer:
Actually the economy today of the USA is very good compared 50 years ago.
Explanation: