The answer is; D
Some plants change color with environmental pH. Examples of such flowers are Hydrangea, Hibiscus, These plants have been used to create litmus paper used in laboratories. In this case, Mary’s plants are blue in acidic pH and turn pink in basic pH. The soil pH makes some nutrients in the soil differentially available to the plants. Depending on which nutrient is made available, such as aluminum, they change color based on its absorption.
