松、竹、梅都有不畏严寒的高洁风格，因而被誉为“岁寒三友”，得到古今文人的广泛赞美．那么这三种植物在分类上分别属于（　　）

    When seven­year­old Sky Nockels learned that black rhinoceroses (犀牛) were an endangered species, he decided to do something to help them. He raised money to adopt (收养) a black rhino named Imara at the Great Plains Zoo in South Dakota. By adopting Imara, Sky helps the zoo take care of the rhino's needs, such as food and a good habitat.

    Sky has been a summer camp member at the Great Plains Zoo since he was three. There he and other kids learnt about the animals and did projects for them. “We made juice drinks for the bears,” says Sky. “They enjoyed them.”

    Now that Sky is older, he is playing an even more active role in the care of the animals. Since black rhinos are one of Sky's favorite animals, he decided to adopt Imara first. “I adopted a Grevy's zebra named Demani, too, for my little brother Alexander,” he says.

    Sky raised money to help care for the animals he wanted to adopt. He promised to raise $75 for his rhino and $25 for Alexander's zebra. To earn the money, Sky and his grandfather planted a vegetable garden. Sky planted seeds (种子), watered, and cleared the grass. When the time came, he harvested the vegetables and sold them in front of his parents' store.

    When Sky's friends heard about this, they brought vegetables from their parents' gardens to sell, too. With the help of his friends, he earned enough money to keep his promises.

    Sky is one of the youngest people to adopt an animal at the Great Plains Zoo. He cares about the animals and plans to plant and sell vegetables again this summer to help them. “I hope other children do something to help animals, too,” he says.

对于函数$y=f\left(x\right)$，如果存在区间$m,n$，同时满足下列条件：①$f\left(x\right)$在$m,n$内是单调的；②当定义域是$m,n$时，$f\left(x\right)$的值域也是$m,n$，则称$m,n$是该函数的“和谐区间”．若函数$f\left(x\right)=\frac{a+1}{a}-\frac{1}{x}\left(a>0\right)$存在“和谐区间”，则$a$的取值范围是(    )