Question

practice it!
which of the following is the independent variable (or test variable) in
the flu-d12 investigation?

the exposure to ultraviolet light

the rate of viral infection

the amount of virus killed

the temperature of the environment

Explanation:

In an experiment, the independent (test) variable is what's manipulated. In a Flu - d12 investigation, "the exposure to ultraviolet light" is likely the factor being changed to observe its effect on virus - related outcomes (like infection rate or virus killed). The other options are either dependent variables (outcomes measured, like infection rate, virus killed) or not the manipulated factor (temperature here isn't the key manipulated variable for Flu - d12 in this context).

Answer:

the exposure to ultraviolet light