The kid was making noise just to attract attention. Let him be!
A. in addition
B. in vain
C. on average
D. on purpose
网友回答
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。