Answer:
A. the bottle with 0% concentration
Explanation:
In teh bottle with the 0% concentration you can create a control observation of the experiement to see how it beheaves even if it has no concentration and if it really depend on the substance added or is something that happens naturally in those environments. Remember that when doing experiments you should always have a sample of the subject that is given nothing in order to observe the normal behaviour of the subject under no studies.
