我国中等收入阶层人数已达3亿，占全球中等收入群体的30%。

A.China's mid-income class has reached 300 million, accounting for 30% of the middle-income group globally.

B.China's mid-income class has reached 3 billion, accounting for 30% of the middle-income group globally.

C.China's mid-income class amounted to 30 million, accounting for 30% of the middle-income group globally.

D.China's mid-income class amounted to 3000 million, accounting for 30% of the middle-income group globally.

正确答案：China's mid-income class has reached 300 million, accounting for 30% of the middle-income group globally.