Wolves live in a world that requ

Wolves live in a world that requires certain predictable kinds of behavior. They must be able to cooperate in the hunt and in (16) their young. Much of their behavior is based on instincts that have served them for (17) generations. But wolves must also be able to learn from observation and from their own experience. They may be (18) with an urge to chase and bite, (19) the actual techniques they use to bring down prey cooperatively are learned from (20) others in the pack and from practice. Experience also helps teach wolves about (21) in their environment, such as steel traps or the guns of hunters.
Over many thousands of years of living with people, dogs have become quite different from their wolf ancestors. Domestication requires the (22) to adapt to different surroundings.Some dogs live with human families (23) pets, with no other dogs around. Others work hard for their human masters, (24) or cooperatively in a group. They usually manage very well to fit into the role expected of them.
In order to be able to make these adaptations, dogs have become very (25); their behavior can be easily molded to fit human needs. In the (26) of adapting to captivity,dogs have also come to depend on humans for their survival and to (27) them for food and for meeting their (28) needs. The dog relies on humans to help it learn what it needs to know, (29) the wolf counts on itself and on its pack mates for new knowledge. The wolf's mentality serves it well in the (30), and the dog's mentality makes it the ideal helpmate for humans. Both animals have the kind of intelligence they need to survive in the environment in which they live.

29.
A、unless
B、because
C、although
D、while
【正确答案】：D