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In English, people say dogs are man's
friends. Dogs and humans have been
for thousands of years. Scientists believe the
is very deep. They found that dogs cry with
when they see their
after being away a
time. The
studied 22 dogs. They looked at how the dogs reacted when they saw their owners
. When the dogs saw their owners, they cried. When
saw other
they knew, they didn't cry.
