They have made so great progress .A. three years agoB. for three yearsC. in the past three

问题补充：

They have made so great progress .

A. three years ago

B. for three years

C. in the past three years

D. before three years

答案：

A. three years ago

B. for three years

(答案→)C. in the past three years

D. before three years

解析：考查时态。“in/over/for+一段时间”常和现在完成时连用。A用于一般过去时。句意“在过去的三年里，他们已经取得了如此大的进步。”故选C。