题干
There are many wetlands（湿地） in China and some of them have become the world‘s important wetlands. The Chinese Yellow Sea Wetlands are among them. They are in Yancheng， Jiangsu Province. They are home for many different kinds of birds and animals. The world’s largest Milu Deer Nature Reserve（自然保护区） is in them. More than 700 milu deer live freely there. There are not many red-crowned cranes in the world， but every winter you can see some in the Red-crowned Cranes Nature Reserve in the Yellow Sea Wetlands.
The temperature in the wetlands is usually neither too high nor too low. There is a lot of rain and sunshine， too. They are really good places for wildlife（野生生物）。 Offering food and home for some special kinds of animals and birds is not the only reason why we need to protect wetlands. Wetlands are important because they also prevent flood. But some people want to change the wetlands to make more space for farms and buildings. This means there will be less and less space for wildlife.
Luckily， more and more people are beginning to realize the important of wetlands and wildlife. Every year， on February 2nd， many activities are held to tell people more about wetlands.
根据以上短文内容，然后从每题所给的四个选项中选择最佳选项。
The temperature in the wetlands is usually neither too high nor too low. There is a lot of rain and sunshine， too. They are really good places for wildlife（野生生物）。 Offering food and home for some special kinds of animals and birds is not the only reason why we need to protect wetlands. Wetlands are important because they also prevent flood. But some people want to change the wetlands to make more space for farms and buildings. This means there will be less and less space for wildlife.
Luckily， more and more people are beginning to realize the important of wetlands and wildlife. Every year， on February 2nd， many activities are held to tell people more about wetlands.
根据以上短文内容，然后从每题所给的四个选项中选择最佳选项。
是偶函数，则常数
的取值范围是( )
