Hemlocks are a common type of tree in the northern forests of the United States. In studying one forest, a forester noticed that mature hemlocks were abundant but there were very few young hemlocks. She wondered why there were so few young hemlocks. By reading the records that other foresters in that area had kept, she learned that the population of deer living in the forest had doubled in the last five years. By reading studies on forests that other scientists had performed, she also learned that deer in similar forests like to eat young hemlocks and the young trees of other species. To test her hypothesis, the forester set up an experiment. She placed fencing around a group of 15 young hemlocks to prevent deer from eating them. She left a group of 15 young trees with no fencing around them. Each day, she examined the trees for evidence that deer had been eating their twigs and branches and counted the number of trees with visible bite marks.

Which example is the control group for this experiment?

the number of young deer in the forest

the young trees without fencing

the number of deer in the forest

the young trees surrounded by fencing