井下防爆电气设备的运行、维护和修理，必须符合防爆性能的各项技术要求。（）
参考答案：对
已知双曲线的中心在原点，一个顶点的坐标是（-3，0），且焦距与实轴长之比为5：3，则双曲线的标准方程是______．
As he works in a remote area, he visits his parents only . [ ]
A. occasionally
B. anxiously
C. practically
D. urgently
