All we really know is that men, unlike animals, somehow invented certain sounds to express thought and feelings, actions and things, so that they could communicate (30)____ each other; and th
All we really know is that men, unlike animals, somehow invented certain sounds to express thought and feelings, actions and things, so that they could communicate (30)____ each other; and that later they agreed upon certain signs, called letters, which could be combined to present those sounds, and which could be written down.
A. upon
B. to
C. about
D. with