Q3:Which of the following is NOT mentioned as a possible source of error in surveying mountain elevation? A. Mirages B. Refraction C. Inaccurate instruments D. Variations in sea level E. Uncertainty about the exact point to be Measured
个人一直徘徊与A和C中, 感觉mirage 和Refraction 重复了, 它是原因更多过与resource of error. 但C好像文中也没提到