Generally speaking, after 4 000 years, on the average, the percentage of the 200 original words which remained in use was ______.

A．After 3 000 years, each daughter language shared only 29% of the basic 200-word vocabulary.
B．Some Aleuts are the descendants of Eskimos on the mainland of Alaska.
C．The language clock can help to determine the dates of certain events.
D．Through thousands of years languages change only in vocabulary.

A．a mechanic clock
B．a figurative clock
C．an electronic clockC. a diamond clock