Concept:To round to 2 significant figures, keep the first two digits and use the third digit to decide whether to round up.Explanation:In 1975, the first two significant digits are 1 and 9, forming 19.The third significant digit is 7.Since 7≥5, we round 19 up to 20.Replace the remaining digits with zeros to preserve place value: 1975≈2000.Answer:D. 2,000