Final answer:
Primate traits selected for life in trees include opposable thumbs and toes, stereoscopic vision, and prehensile tails, rather than large body size.
Step-by-step explanation:
The traits that are believed to have been selected for life in trees among primates are opposable thumbs and toes, stereoscopic vision, and sometimes prehensile tails. These adaptations evolved to improve their abilities in an arboreal environment. The opposable thumbs and big toes enable primates to grasp and manipulate objects more precisely and grip branches securely. Stereoscopic vision greatly enhances depth perception which is critical when moving among trees.
Not all primates have a prehensile tail, but for those that do, it serves as an additional limb for climbing and maneuvering through the treetops. While large body size is not specifically an arboreal adaptation, other aspects of primate morphology like rotating shoulder joints and the trend towards an upright posture also support arboreal life. However, for the given options, large body size is not commonly considered a trait selected for arboreal life.