Which statement about the use of independent variables in controlled experiments is correct? 1.

A different independent variable must be used each time an experiment is repeated.

2.

The independent variables must involve time.

3.

Only one independent variable is used for each experiment.

4.

The independent variables state the problem being tested.

3. Only one independent variable is used for each experiment.

Explanation:

A controlled experiment is an experiment in which one variable is changed or tested at a time, while others are kept constant. In an experiment, one of the two major variables is INDEPENDENT VARIABLE. Independent variable is the variable that is changed or manipulated in the experiment.

In a controlled experiment, only one independent variable is used at a time i.e. ONLY one variable is changed or manipulated for each experiment. This is to ensure the validity of the experiment.

good one: produce hormones that plants grow.

bad one: the problem with organic matter is that while plant nutrients are needed for crop growth, they can also stimulate excessive growth of the wrong plants – mainly, algae.