Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…H. Dong (&) Y. Niu X. Kong Z. Luo Cotton Research Center, Shandong Academy of Agricultural Sciences, 250100 Jinan, Shandong, China e-mail: donghz@saas.ac.cn
condition to study association between source and sink, as well as vegetative and reproductive growth (Dong et al. 2008b; Zhang et al. 2008).
Category: