Questions: When carrying out a controlled experiment, it is important to: change multiple variables at once to see the full effect of the variables. All of these choices are correct. subject different groups to different conditions. change only one variable at a time.

In a controlled experiment, it is crucial to change only one variable at a time while keeping all other conditions constant. This approach allows researchers to isolate the effects of the independent variable on the dependent variable, ensuring that any observed changes in the dependent variable can be attributed to the manipulation of the independent variable.

Explanation:

1. Subject different groups to different conditions: This is partially correct. In a controlled experiment, you typically have at least two groups: the experimental group, which is exposed to the independent variable, and the control group, which is not. The purpose of having different groups is to compare the outcomes and determine the effect of the independent variable. However, the key is that within each group, only one variable should be changed at a time.

2. Change only one variable at a time: This is the correct principle for conducting a controlled experiment. By changing only one variable, researchers can confidently attribute any differences in the results to the variable being tested. This helps in maintaining the integrity of the experiment and ensures that the results are due to the variable of interest rather than other confounding factors.

In summary, while it is important to subject different groups to different conditions, the core principle of a controlled experiment is to change only one variable at a time to accurately assess its impact.