单项选择题

TEXT D
It takes about $400 worth of equipment to climb a tree--arborist ropes, helmet, climbing saddle, metal loops called carabiners. But when you’re 100 feet up or so and your perch is swaying in the wind, you’ll be glad you came prepared.
Mr. Teitelbaum is part of a small but growing community of adults who call themselves recreational tree climbers. He has even found a business in it, teaching others through his company, Tree Climbing Colorado.
Although data about the participants are difficult to come by, New Tribe, an Oregon company that sells equipment for recreational tree climbing, says it has sold almost 1,500 tree-climbing saddles this year, up 34 percent from 2004.
Some ground dwellers might consider these climbers slightly less evolved than monkeys (Mr. Teitelbaum’s father has half-teasingly asked his son to change his last name to save the family embarrassment); but Mr. Teitelbaum and his colleagues happily spend their leisure hours climbing, and even sometimes camping, in trees.
Using ropes and other climbing gear, they sway from branches for hours, talking to the tree, hugging it, getting a unique perspective on the world. Everyday worries seem to disappear, they say. Mr. Teitelbaum does not consider himself an extreme-sports kind of guy. He just likes being in the trees.
For safety and camaraderie, Mr. Teitelbaum prefers climbing with someone else, although he can’t always find a partner. He has never been stranded, but he carries a cell phone just in case. His wife does not climb very much. This time, he had agreed to take along a reporter interested in finding out how tree climbing feels firsthand.
Mr. Teitelbaum looked things over, something like a pilot looking over a plane. He did a three-point check--the ground, the trunk and the canopy--looking for damaged or exposed roots, fungus, glass, nails, power lines, hollows or missing bark, trunk splits, insects, animals, dead or dying growth, tree lean or anything else that might pose a danger.
Wearing a climbing helmet over his gray hair, he repeatedly emphasized safety, saying, "We don’t want people killing themselves." He is a graduate of a recreational tree-climbing certification program run by Tree Climbing International, an Atlanta-based umbrella organization for recreational tree climbers. In his own $400 course, he trains people over a weekend, ending in a written test and a climbing test.
To secure safety, Mr. Teitelbaum does all of the following EXCEPT that ______.