Biology

The correct answer is: all variables are constant except the one you are testing.

Here’s why:

In a controlled experiment, the goal is to isolate the effect of the independent variable (the one you are testing) on the dependent variable (the outcome you are measuring). To achieve this, all other variables that could potentially influence the outcome are kept constant or controlled. This ensures that any observed changes in the dependent variable are due to the manipulation of the independent variable alone.

Let’s evaluate the other options:

B.More than one variable can be tested at a time: In a controlled experiment, you typically test only one independent variable at a time. If you test multiple variables simultaneously, it becomes difficult to determine which varia...