单选题 Radar is used to extend the ______ of man's senses for observing his environment, especially the sense of vision.
  • A. validity
  • B. liability
  • C. capacity
  • D. intensity
【正确答案】 D
【答案解析】[解析] 各项的意思为：validity有效性，合法性；liability责任，负债；capacity容量，地位；intensity强烈，强度。答案是D。