Answer: He could add a base to the pool to neutralize the acid.
Explanation:
Chlorine is used to disinfect the pools as it produces hypochlorous acid in water. This hypochlorous acid is unstable and gives hydrochloric acid and nascent oxygen which is used to disinfect.

The excess acid is neutralized by adding base which produces salt and water and thus decrease the acidity.

Adding more acid would increase the acidity further.
Answer: Pure substances are further broken down into elements and compounds. Mixtures are physically combined structures that can be separated into their original components. A mixture is composed of different types of atoms or molecules that are not chemically bonded.
Explanation:
Answer:
Living beings and non-living things both follows the physical and chemical general principles, like the thermodynamic laws, and they are constituted both by atoms and molecules, the basis of the natural organization of all known matter on Earth.
I would say D.
A is incorrect by simple reasoning.
B is also incorrect. A hypothesis is made before evidence supports it, therefore, it doesn't matter if all evidence supports it, as it shows an guess. It sometimes can also lead to more experimentation even if it's not true for the current experiment.
C is also incorrect. An untestable hypothesis isn't useful as you cannot test anything relating to it, and it cannot be proven or disproven.
Hope this helps!