Biology

A: A control group and an experimental group are fundamental.

The control group provides a baseline for comparison, allowing researchers to isolate the effect of the treatment (in the experimental group).
For example, in an experiment testing the effect of a new drug on blood pressure, the control group would receive a placebo while the experimental group gets the drug.

B: Random assignment helps to reduce bias.

If samples are not randomly assigned, there could be pre - existing differences between the groups that might confound the results.
For instance, if you're studying the effect of a fertilizer on plant growth and you non - randomly assign larger plants to the experimental group, it will be hard to tell if any growth differences are due to the fertilizer or the initial plant size.

C: In a well - designed controlled experiment, it's best to manipula...