Why are police dogs good at smelling?

Police dogs are specially trained to smell specific things for example, drugs. All dogs have a great sense of smell, but police dogs are trained specially for smelling purpose.

coqbc2000 講的對
use the word ' sniff '
嗅毒犬 = drug sniffing dog

Is it more appropriate to use the word "SNIFF" instead of "smell"?

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not just police dogs are good at smelling,all dogs have a great sense of smell.
every dog are the same because dogs eyes is not good as people so they use smelling to reconise were they are and thing they touch.Dog sees every thing is black.

every dog are the same because dogs eyes is not good as people so they use smelling to reconise were they are and thing they touch.Dog sees every thing is black.

not just police dogs are good at smelling,all dogs have a great sense of smell.