The control in experiments is a sample that remains the same throughout the experiment and it is used to compare the results of the main experiment to. It serves to guarantee that changes noted in the experiment are from the variables introduced and not something else.
<h2>Answer:</h2><h3>1. Hepatitis B </h3><h3>2. Levels of circulating antibodies against a certain antigen.</h3><h2>Explanation:</h2><h3>Hope its help</h3>
