Which of the following is the best example of a noninvasive research method for studying primates?​

A) ​drawing blood for analysis
B) ​caging primates separately to enforce language learning
C) ​restructuring primate family groups to study social behavior
D) ​taking fecal samples to study diet and health

Taking fecal samples is a noninvasive method for studying diet and health in primates. It does not require physically interacting with or harming the animal. Drawing blood (A) and restructuring family groups (C) can both be considered invasive as they involve physically manipulating the animals. Caging primates separately (B) is unethical and potentially harmful to the animals.