APA

lauber p., keller h., . (1994). be a friend to trees. new york: harper collins.

Chicago

lauber patricia, keller holly, . 1994. be a friend to trees. new york: harper collins.

Harvard

lauber p., keller h., . (1994). be a friend to trees. new york: harper collins.

MLA

lauber patricia, keller holly, . be a friend to trees. new york: harper collins. 1994.