Final answer:
The most energy-efficient form of locomotion at a normal walking speed is walking bipedally, due to efficient kinetic energy transfer and anatomical adaptations for balance.
Step-by-step explanation:
The most energy-efficient method of locomotion at a normal walking speed is B) walking bipedally. This is because bipedal locomotion allows for an efficient transfer of kinetic energy as the individual's legs alternate between being the stance leg and the step leg. Additionally, humans and other bipedal organisms have undergone various anatomical adaptations to maintain balance and reduce energy expenditure while moving on two legs. In contrast, knuckle walking, quadrupedal walking, and walking on two hands are less efficient at normal walking speeds due to less optimal energy transfer and balance mechanisms.