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

Dr. Gilbert was the land manager for a prairie that had become overrun by unwanted grasses. These grasses crowded out other plants. Dr. Gilbert thought that she could use fire to remove the unwanted grasses and allow other plants to grow. But she didn't know how often the prairie should be burned.
Dr. Gilbert marked off six plots within a large area of the prairie. She used carefully controlled fires to burn all of the plants in each plot. She burned three of the plots once a year for three years. She burned the other three plots twice a year for three years. A year after the last fire, Dr. Gilbert counted the number of unwanted grasses in each of the six plots.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: a fire burning through a prairie.
Which of the following was a dependent variable in this experiment?
A. the number of unwanted grasses
B. the number of times the plots were burned each year
Pick the correct answer from the listed options and provide the letter of the selected option.

A