Dogs have been man's good friengs for t__ of years.Many stories told how brave dogs helped people in t____.With the help od dogs,many people l___ in snow found their way home.
Dogs have also helped in many scientific researches.The first spacetraveller was a dog n___ Laika.It was sent up in a manmade earth satellite in 1957 by R____ scientists.
Dogs have become film stars,too.A dog called Lassie was the star in quite a few American f____.
Dogs can h___ and s___ better than man,but they can not see so well.A dog may l____ for about 12 or 13 years.A thirteen-year-old dog is a very old dog indeed.

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