问题补充：
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．
smaller
答案：
(答案→)smaller
解析：
【小题1】根据第一行的is becoming smaller every year可知，鸟的数量正在减少，故填smaller。
【小题1】根据最后一段第二行They are in danger from traffic可知，填danger。
【小题1】根据第二段第一行about two—thirds are allowed to go outside可知，填allowed。
【小题1】根据最后一段的最后一句If you raise a young cat, it’s your duty to let it play inside.可知，填raise。
【小题1】根据最后一段的最后一句可知，养猫的人有责任让猫待在家里。故填duty。
