从环境保护的角度来看，最理想的能源是(    )

阅读下面的文字，完成下列小题。

                                                                                    清晨我漫步在山坡谷地，

                                                                                    晨光宣泄着永恒的秘密，

                                                                                    山涧里流倘出一条小溪，

                                                                                    她在歌、在唤、在吐露心曲：

                                                                                    生活并非安逸，

                                                                                    它是思念和希冀。

                                                                                    死亡并非哀歌，

                                                                                    它是失望与憔悴。

                                                                                    智者不在言词，

                                                                                    其秘密在言词背后藏nì。

                                                                                    伟人不在高位，

                                                                                    不屑权位者才配享荣誉。

                                                                                   （纪伯伦《小溪，你说什么》节选）

关于x，y的方程$\frac{x^2}{5-m}+\frac{y^2}{2+m}=1$满足下列曲线，分别求m的取值范围：

（1）焦点在x轴的椭圆；

（2）焦点在y的双曲线．