in the southwestern section of texas, the major international crossing along
u. s.-mexican border is what?

b. they require a huge investment of time, dedication ,training, and patience almost from the day they are born.

explanation:

the sentence gives a clear evidence of how carefully the sar dogs are selected and also specify from what time this exercise begins."almost from the day they are are born." this sentence shows as that this exercise begins early.

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there purpose is to entertain