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.
Answer:
Legume crops improve soil health, they add nitrogen and organic matter to the soil and reduces potential erosion and leaching loss. Legumes may reduce the energy footprint of cropping systems by reducing the need for nitrogen fertilizer, and improve the stability and health of agro-ecosystems.