observing changes in a single trial. testing for a desired trait. repeating steps in a procedure. controlling changes in conditions.
I gave my students this multiple choice question: Scientists study the reaction of some bacteria to antibiotics, hoping to learn about a new strain of resistant bacteria. This method of gaining scientific knowledge is best described as

Only one answer is correct among these 4 choices:
- observing changes in a single trial.
- testing for a desired trait.
- repeating steps in a procedure.
- controlling changes in conditions.

Could you tell me which one is correct?

testing for a desired trait.