Which adaptation makes bipedalism possible?

By walking on two feet, also since our morphological features, especially our eyes, hands and other parts are towards the frontal phase.
This is also an intellectual advantage for most humans since when we are upward we can better see our surroundings, seem bigger and taller, can detect preys and other mechanisms for survival.

Adaptations are the result of evolution in different living organisms. This process occurs amazingly through gene mutation but it takes a very long period in time. Adaptation processes occur to help species survive and thrive in the ecological balance of life. Structural adaptations are physical features of an organism that adapted through time. An example of this are the bills of a bird and the fur of bears that they generally need for their survival; birds for hunting, and bears to protect them from low climate areas.

The answer is option b.