Final answer:
The correct statement about Homo erectus is that they were fully upright, lived on the ground, traveled easily, and had mastered the use of fire. Other options are incorrect; their brain size was smaller than modern humans, and they indeed mastered fire and left the tropics.
Step-by-step explanation:
The characteristics of Homo erectus include being fully stable on their feet, living on the ground, and traveling rather easily. They did indeed walk upright, making the answer (a) incorrect. They also demonstrated mastery in the use of fire which allowed them to leave the tropics, making answer (b) incorrect. Answer (c) is also incorrect as their brain was smaller than those of modern humans. Thus, the correct answer to the question is (d) 'Were fully stable on their feet, lived on the ground, could travel rather easily, and had mastered the use of fire.' Homo erectus was an early human species that possessed numerous similarities with modern humans, including stature, brain size, and behaviors such as tool-making and use of fire for warmth and cooking food. They reached heights comparable to modern humans and had brains that were three-fourths the size of modern human brains, disproving option (c). They lived until as recently as 50,000 years ago in some regions, having a significant impact on the course of human evolution.