Question

What is the most difficult part of a controlled experiment?

Answer 1

Answer:

The correct answer is option 1.) "testing only one variable".

Explanation:

One of the basis of scientific experimentation is to test one variable at the time in order to make sure that the obtained results are a direct consequence of the variable of study. However, testing only one variable at the time is not an easy task. It is necessary to establish a negative control which only difference is the absence of the variable, and a positive control using a variable that the scientist know is going to produce a response.

Answer 2

1. Testing only one variable
A controlled variable means its the one that stays the same. In a controlled experiment, it means there is only one manipulated, (changed) variable.