Trainers reward the monkeys by using positive reinforcement, such as food, drink, praise, and ____(感情) .
For example, compared with humans, dogs are “far superior at tracking down odors,” says Marian Bailey, an animal ____(行为科学家) at Henderson State University in Arkansas.
“Dogs love to retrieve objects so the towel becomes a reward,” says Morris Berkowitz, who heads up a ____(犬的) drug-sniffing program in New York.