Why do biological classification keys always present only two choice at each step? btw i am doing a shark dichotomous key analysis

Because it is simple, and more capable way of separating organisms.

Explanation:

A biological key is also known as dichotomous key or identification key, which helps to classify the organisms by giving classifier two options in each stage until the identification occurs.

The biological classification key always present only two choices at each step, because it is simple and more capable way of separating organisms without confusion. Dichotomous means breaks into two parts and that's why dichotomous always gives two choices at each stage. In each step, the user is represent with the two statements based on the characteristics of the organisms.

the answer is

c. parental