Read the following excerpt from the article "Volunteers Count Every Street Tree in New York City." As you read, think about which statements are opinions and which ones are facts. Did you know? Over 80 percent of the U. S. population lives in cities or metropolitan areas, making urban trees more important than ever. Trees bring many benefits to human health--they filter air pollution, release oxygen, reduce mental stress, and absorb rainwater and noise. Trees in cities connect rural forests and parks to the urban landscape, creating habitat linkages for wildlife species like migratory birds. These are some of the many reasons the U. S. Forest Service supports trees in urban areas, and why the City of New York has been recruiting residents to count its trees for decades.

Which of these statements is an opinion?

a. "Trees in cities connect rural forests and parks to the urban landscape. . . ."
b. "[U]rban trees [are] more important than ever."
c. "Over 80 percent of the U. S. population lives in cities or metropolitan areas. . . ."
d. "Trees bring many benefits to human health. . . ."