Answer:
Let's add the options to complete the question
-He could change the dependent variable to amount of shade and set up shade umbrellas over ten of the plants.
-He could change the independent variable to amount of sunlight and trim taller plants nearby so ten of the plants are no longer shaded.
-He could add more controls so there is less chance that other factors are contributing to the mold growth.
-He could change the timing of data collection so he is recording observations every two days for two full months.
The CORRECT ANSWER IS
-He could change the independent variable to amount of sunlight and trim taller plants nearby so ten of the plants are no longer shaded.