Complex sentence: When questioned, Kuo mentioned that his factory is not the only one producing lard oil from ill livestock, but stated that around 10 factories in Yunlin, Taichung, Tainan, Kaohsiung, and Pingtung also produced oil in this manner.
Split into simpler sentences: When questioned, Kuo mentioned that his factory is not the only one producing lard oil from ill livestock. Kuo stated that around 10 factories in Yunlin, Taichung, Tainan, Kaohsiung, and Pingtung also produced oil in this manner.