We often plant trees every year.A. thousandB. thousand ofC. thousands ofD. thousands

问题补充：

We often plant trees every year.

A. thousand

B. thousand of

C. thousands of

D. thousands

答案：

A. thousand

B. thousand of

(答案→)C. thousands of

D. thousands

解析：thousands of 表示成千上万的，为故定词组搭配，故选C，符合题意。