Fossilised foot bones of domesticated cattle from prehistoric European villages prove that cattle were used as traction engines as early as 8000 years ago. These footbones are wider than those of the wild cattle which lived in the same area around the same time.
Which of the following is an assumption involved in the argument above?
A. Where the fossilised bones were found determined whether the cattle were wild or domesticated.
B. Originally, cattle were domesticated in order to ensure a regular supply of milk and beef.
C. Use of cattle as traction engines is best evidenced by the remnants of prehistoric plows.
D. Carrying more than its own bodyweight can lead to skeletal changes in a quadruped.
E. In the absence of proper roads, helping humans with transportation must have been an arduous job for the domesticated cattle of prehistoric times.