A. Its origin is not obscure. B. It’s possible for apes to speak human language, but an intensive professional instruction is necessary. C. There are people who doubt that it began very gradually. D. It has been the most important single factor in the development of man.
A. Its origin is not obscure.
B. It’s possible for apes to speak human language, but an intensive professional instruction is necessary.
C. There are people who doubt that it began very gradually.
D. It has been the most important single factor in the development of man.