Complex systems of written characters were developed in the Huang He and Yangtze River Valleys __________.
A.
by the Sumerian civilization
B.
by the ancient Egyptians
C.
by the Toltec civilization
D.
during the Shang dynasty
A.
by the Sumerian civilization
B.
by the ancient Egyptians
C.
by the Toltec civilization
D.
during the Shang dynasty