Question

why cant more than one variable be changed during an experiment? *
you need to make sure your results match your hypothesis.
changing two or more variables makes it difficult to find a cause and effect relationship.
change two or more variables would take longer.
changing two or more variables would make the experiment more precise.

Explanation:

In an experiment, the goal is to determine cause - and - effect relationships. Changing multiple variables simultaneously makes it impossible to tell which variable is responsible for the observed results.

Answer:

Changing two or more variables makes it difficult to find a cause and effect relationship.