What is the most logical next event?

How to test the acidity of your rain
Gather the necessary materials.
For this experiment, you will need to collect some rain water and get some strips of ph paper. Ph paper is a special type of paper that changes color based on how acidic or basic a solution is.

Choices:
A). River banks are the best places to find ph paper. Testing water for ph can be expensive and will require significant research..
B). There are two sizes of ph paper you will need for this experiment. Ph paper has a diameter of 3 to 4 inches..
C). These test strips are available at different labs or at online testing facilities. You can purchase ph paper at your local academic library..
D). The paper comes with a separate color chart that allows you to identify the ph according to the color. Ph paper can be purchased at gardening or pool stores..
D).