The oldest known transport wheel was discovered in 2002 in Slovenia. It is over 5,100 years old. Evidence suggests that wheels for transport didn’t become popular for a while, though. This could be because animals did a perfectly good job of carrying farming tools and humans around.Q: What might explain why transport wheels didn’t become popular for some time?

A. Few knew how to use transport wheels.
B. Humans carried farming tools just as well.
C. Animals were a good means of transport.
D. The existence of transport wheels was not known.