The kid was making noise just to attract attention. Let him be!A. in additionB. in vainC.

问题补充：

The kid was making noise just to attract attention. Let him be!

A. in addition

B. in vain

C. on average

D. on purpose

答案：

A. in addition

B. in vain

C. on average

(答案→)D. on purpose

解析：考查短语辨析。in addition此外，in vain白费力，on average按平均计算，on purpose故意的，根据句意孩子们故意发出噪音仅仅是引起注意。故选D。