—What does PM2.5 mean?—It's a professional indicating the condition of air pollution.A. t

问题补充：

—What does PM2.5 mean?

—Its a professional indicating the condition of air pollution.

A. term

B. item

C. number

D. mark

答案：

(答案→)A. term

B. item

C. number

D. mark

解析：A 考察名词辨析。句义：—PM2.5什么意思啊？—那是一个标明空气状况的专业术语。Term意为“术语”，符合题意。BCD三项与句义不符。故A正确。