contribution,contributions
同一篇文章中有的地方用contribution,有的地方用contributions,请分析下,
I would like to thank Mr Tan Tat Chu,Paul Tan,Ms Yuan Jiang and Ian Martin at Thomson Learning Asia for their contribution to the project.
...
Additional thanks to Robert Lee for contributing his skill as singer/musician to the series,and to Zhang Linlin,Lu Xiqin and Guo Juan for their valuable contributions.