According to the british anatomist wilfrid le gros clark, the main tendencies that to define what a primate is include a. parental investment; similar dental specializations; and small brains. b. all of the choices are correct. c. prehensile fingers, toes, and tails; dietary plasticity; and enhanced sense of vision. d. the ability to eat a wide variety of foods; investing time and effort into offspring; and adaptations to life in the trees.

The correct option is D.
According to the British Anatomist, primates have these three distinguishing characteristics"
1. Primates eat a wide variety of food, that is, they exhibit dietary plasticity. 
2. Primates are adapted to living on trees. Primates have specific anatomical structures and behavior which adapted them to living on trees.
3. Primate put in a lot of time in taking care of their offspring. Primate usually give birth to few children but they invest time in taking care of their children.

I’m going to go with b!