【单选题】

1 Play is common to the young of most mammals. Some birds play, but it is rare in cold-blooded animals such as fish and reptiles. Why some animals play, and others do not, is not entirely understood, but the most playful--such as dolphins and monkeys--are also the most intelligent and sociable. Play may seem something of a puzzle. Not only is it apparently unproductive, but it also places the participant at risk of being surprised by predators. However, there must be a good reason for play. The most widely held scientific explanation is that play allows the social behaviors of the species to be explored and learneD、Other benefits include physical exercise and the learning of survival skills such as hunting.

A、kitten that grows up separated from other kittens becomes both a social misfit and a poor hunter, largely because it is deprived of play.
2 Kittens start playing when they are about three weeks olD、Early play consists of mock attacks with the mother and littermates, clearly previewing the territorial behavior of adult life.As the kittens grow older, more elaborate play patterns develop.At four weeks they can wrestle. The sideways leap and the pounce may be learned by the fifth week.By six weeks they can chase and leap on each other with reasonable accuracy. Kittens stalk, chase, and fall over each other. They recognize these patterns as being playful, even though the same signals in adult life may have a more serious meaning.
The author mentions dolphins and monkeys as examples of
A、rare species
B．fish and reptiles
C．playful animals
D．predators