以下哪项（ ）有利于节约能源 Which of the following suits for energy-saving（ ）

A、对供冷供热管线进行保温 Making thermal insulation for cooling and heating pipelines
B、以矿产资源代替废金属资源生产金属材料 Producing metal materials with mineral resource instead of metal scrapes
C、长距离输送电力 Long distance transmission of electric power
D、尽多采用空调系统 Using air conditioning system as much as possible