trees are cut down in the forests every year.A. ThousandB. ThousandsC. Thousands ofD. Tho

问题补充：

trees are cut down in the forests every year.

A. Thousand

B. Thousands

C. Thousands of

D. Thousand of

答案：

A. Thousand

B. Thousands

(答案→)C. Thousands of

D. Thousand of

解析：句意：每年森林里都有成千上万的树木被砍伐。Thousands of“成千上万的”。故选C。