Answer:
The options to this question are;
A. genotype
B. adaptation
C. selective pressure
D. stabilizing pressure
The answer is B) Adaptation
Step-by-step explanation:
Adaptation is the process whereby an organism becomes well suited to survive in its natural environment, which is aided by the possession of certain traits called adaptive features. For example, the fins of a fish makes it fit to survive in an aquatic environment, likewise the opposable thumbs of humans make us well suited to survive in our environment.
As stated in the question, the opposable thumb i.e. movement of the thumb independently of the other four fingers, is a characteristics of primates. This unique feature (opposable thumb) allows us to grab things, get a good grasp of tools, use tools effectively, write things, etc. All these ability due to the possession of opposable thumb increases our chances of survival. Hence, the possession of opposable thumb is regarded as an ADAPTATION