Polio viruses contain DNA. The viruses in the polio vaccine have DNA in which the base sequence has several differences from the base sequence in the normal polio virus. Suggest how this makes them unable to reproduce in the human body.

Ruby is conducting an investigation. an advantage of her design is that she can use a large range of variables, with that she can not be sure that one variable is the cause of another. what kind of investigation is ruby most likely conducting?