In which situation has the independent variable for the experiment been changed?

Check all that apply.

I changed from counting the number of duckweed at day 0 and day 14 to counting them every day

I changed from testing duckweed growth in beakers to testing duckweed growth in large outdoor

tanks

changed from testing the effect of pH on duckweed growth to testing the effect of light levels on

duckweed growth

changed from testing the effect of acid pH on duckweed growth to testing the effect of basic pH on

duckweed growth

changed from testing the effect of pH on duckweed growth to testing the effect of light levels on duckweed growth

Explanation:

There are at least two variables in every experiment. The independent variable and the dependent variable. The independent variable is manipulated and its effect on the dependent variable is evaluated.

pH and light levels are both independent variables. When one switches from testing the effect of one of them on duckweed growth to testing the effect of the other, then a change in independent variable has occurred.