19.
(A) Already in the Paleolithic Age, tens of thousands of years ago, the ancient Chinese knew
how to make simple tools and ornaments from animal bones and tusks.
(B) Already in the Paleolithic Age, millions of years ago, the ancient Chinese knew how to
make simple tools and ornaments from animal bones and tusks.
(C) By the Paleolithic Age, tens of thousands of years ago, the ancient Chinese were known
how to make simple tools and ornaments from animal bones and tusks.
(D) By the Paleolithic Age, millions of years ago, the ancient Chinese were known to have been
making simple tools and ornaments from animal bones and tusks.