Are sniffer dogs at customs there for sniffing explosives or drugs?

i heard that sniffer dogs vary. That they are either sniffer dogs for explosives or for drugs. Even with drugs, some dogs only are trained to only sniff out certain drugs. what kind of sniffer dogs are at the customs at the airports?
Update: the dog i seen was a germain shepard.
will that tell me if the dog is a drug sniffer dog or a explosive and money finding one?
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