Pre-australopiths experienced environmental cooling that, over thousands of years, converted large parts of their african habitat from forest to savannah grassland. which adaptation emerged during this time to become one of the key distinguishing characteristics of our ancestors

Bipedalism is the adaptation which emerged during pre-australopiths so as to become one of the key distinguishing characteristics of our ancestors.

Bipedalism is known as a form of terrestrial locomotion whereby organisms moves by means of its two rear legs or limbs. By freeing their front legs, our ancestors had a benefit like allowing the use of carrying tools.
 Walking upright helped the ancestors to be able to see the predators and the preys.

The  correct answer should be a waste