Context: The passage below describes an experiment. Read the passage and think about the variables that are described.

Donald was baking cupcakes for his stepfather's birthday. Donald wondered whether the volume of a cupcake would be affected by the type of flour in the batter.
Donald bought three types of flour and made three batches of cupcakes. He followed the same recipe for each batch, except for the type of flour used. He made one batch using whole wheat flour, one batch using cake flour, and one batch using buckwheat flour. After all the batches had baked and cooled, Donald measured the dimensions of each cupcake to calculate its volume.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: cupcakes in a pan.
Which of the following was an independent variable in this experiment?
A. the type of flour used
B. the volume of the cupcakes
Identify the correct option from the choices provided and respond with the letter of the correct option.

A