Answer:
The correct answer is b. morphological
Step-by-step explanation:
Morphological species concept is also known as phenetic species concept. According to this concept if the organisms which are phenotypically (morphologically, anatomically and physiologically) similar are considered to be one species even if they are prevented to mate in between.
All the observable characters come under phenetic characters. For example, if two rhinos look same because they have horns they will be put in the same species even if they do not mate.
Therefore, the morphological species concept defines species boundaries based on the physical characteristics of populations.