Many kinds of birds live in the United States, but the number of the birds is becoming smaller every year. One of the leading reasons is the growing number of pet cats. By keeping your pet cats in your home, you can help give birds a better possible chance to live. Of the 90 million pet cats in this country, about two—thirds are allowed to go outside. It is said that these cats kill hundreds of millions of birds each year, as well as billions of small animals such as rabbits and field mice. They can also bring illness to the animals that live in people’s yard(院子), further weakening the health of the natural populations. Allowing pet cats to go outside is not just bad for birds and wildlife, it’s also bad for the cats themselves. Outdoor cats can get sick very easily. They are in danger from traffic and attacks(攻击)from other animals. In fact, outdoor cats usually don’t live past the age of five, while indoor cats often live to be 17 or older. Keep your pet cat inside! If you raise a young cat, it’s your duty to let it play inside. Problem The number of birds is becoming 小题1:________; at the same time，many pet cats are in 小题2:_______from traffic and attacks from other animals． Reason for the problem Pet cats are小题3:_________to go outside freely． What to do People who小题4:_________ a young cat have the小题5:________  to let it play inside．