Which attribute of H. erectus suggests they were adept at movement across open land?

The correct attribute that suggests Homo erectus was adept at movement across open land is short arms. Short arms relative to body size indicate a more efficient bipedal locomotion suited for traveling long distances on two legs, which is advantageous for a species that may have hunted and foraged in open environments. This adaptation reflects a shift towards a more modern body plan, supporting sustained activity and enabling greater mobility in savanna-like habitats.

In contrast, long arms would suggest adaptations more suitable for tree climbing or arboreal activity, which is not predominant in H. erectus. Broad shoulders generally facilitate climbing and locomotion through trees rather than efficient movement across land. Similarly, a wide pelvis might support bipedal locomotion but is often more related to childbirth in relation to body size than to open land mobility. Hence, short arms are the most indicative of an adaptation for open land movement in H. erectus.