单项选择;从每小题A、B、C、D中选出一个能填入句中空白处的最佳答案。
Sam is doing some ______ about the ancient Silk Road.
A. exercise B. operations C. research D. experiments
单项选择;从每小题A、B、C、D中选出一个能填入句中空白处的最佳答案。
Sam is doing some ______ about the ancient Silk Road.
A. exercise B. operations C. research D. experiments
C