The right answer is a. they contain many small, repeating subunits bonded together.
In chemistry and biology, a polymer is a molecule made up of a chain of similar molecules, called monomers; a polymer is a macromolecule resulting from the assembly of many identical units (monomers), a chemical compound with repetitive structural units.
DNA, glycogen and proteins are polymers
The pH of the stomach in the digestive system is known to be very low, and acidic, so it can break the bonds between molecules, to which the nutrients diffuse into your blood, energizing you.
Among the given choices, the only positive effect that may be thought off with the increase in level of CO2 in the atmosphere is the increase of plant growth. Carbon dioxide is an essential compound in the photosynthesis of plants. Therefore, the answer should be letter C.