The Japanese Macaca monkey has been studied in the wild for over 50 years. In 1952, on one small Japanese island, scientists dropped some   36    dirt for the monkeys. The monkeys liked their taste, but they found the dirt   37  .
One clever 18-month-old monkey    38   the problem by washing the sweet potatoes in a nearby river, She taught this to her mother. Her   39   also learned this new way and they taught their mothers too.
All the younger monkeys   40   learned to wash the dirty sweet potatoes to make them   40   to eat. But many found it very hard to learn this and still ate the   42   sweet optatoes.
Then something very    43   . In the autumn of 1958, scientists found that the monkeys on other nearby   44   began washing their sweet potatoes too. Scientists still don’t fully understand how this knowledge was   45   from one island to another.

A．sweet potatoes B．green plants C．hard stones D．fresh nuts

A．beautiful B．terrible C．difficult D．interesting

A．find B．reach C．solve D．understand

A．children B．brothers C．sisters D．friends

A．quietly B．esily C．angrily D．awfully

A．nicer B．smaller C．lighter D．drier

A．small B．large C．new D．dirty

A．took on B．took off C．took place D．took away

A．trees B．islands C．beaches D．rivers

A．lost B．dropped C．passed D．left