Question: Which city was formerly of Shazhou County, Gao'an or Zhangjiagang?

full_context: Document 1: Gao County: Gao County or Gaoxian is a county of Sichuan Province, China. It is under the administration of Yibin city.
Document 2: Chuzhou: Chuzhou () is a prefecture-level city in eastern Anhui Province, China. It borders the provincial capital of Hefei to the southwest, Huainan to the west, Bengbu to the northwest, Chaohu to the south, and the province of Jiangsu to the east. According to the 2010 Census, the city of Chuzhou has a registered population of 3,937,868 inhabitants, whom 562,321 lived in the built-up ("or metro") area made of 2 urban districts. Nevertheless, 7,260,240 persons declared to be permanent residents.
Document 3: Gaoyao District: Gaoyao, formerly romanized as Koyiu, is an urban district of Zhaoqing in western Guangdong, China. Population: 706,000.
Document 4: Ruichang: Ruichang () is a county-level city under the jurisdiction of Jiujiang, in the north of China's Jiangxi province, along the Yangtze River.
Document 5: Yizheng: Yizheng () is a county-level city under the administration of Yangzhou, Jiangsu province, China, with a population of about 600,000 (2007). It borders the prefecture-level divisions of Chuzhou (Anhui) to the north and Nanjing to the west.
Document 6: Zhaoqing: Zhaoqing, formerly romanized as Shiuhing, is a prefecture-level city in Guangdong Province, China. During the 2010 census, its population was 3,918,467, with 1,232,462 living in the urbanized areas of Duanzhou District and Gaoyao County. The prefectural seat—excluding Seven Star Crags—is fairly flat, but thickly forested mountains lie just outside its limits. Numerous rice paddies and aquaculture ponds are found on the outskirts of the city. Sihui and the southern districts of the prefecture are considered part of the Pearl River Delta.
Document 7: Guangchang County: Guangchang County lies in the municipal region of Fuzhou (抚州), Jiangxi. It is the southernmost and most remote of Fuzhou's ten counties, being bordered by counties in Ganzhou to the south and west and, to the east and over the watershed and provincial border, by Jianning and Ninghua Counties, Sanming, FJ. It is the birthplace of he second largest river in Jiangxi: Fuhe. This county built in the Southern Song Dynasty Shaoxing eight years (1138), because the rich white lotus, known as "the hometown of Chinese White Lotus." County has width of 45 km from west to east, 55 km long from north to south. The total area is 1612 square kilometers, with a population of 240,000 in 2003.
Document 8: Liyang: Liyang () is a county-level city under the administration of Changzhou in the Jiangsu province of the People's Republic of China. In 2011, it had a population of about 781,500. It borders the prefecture-level divisions of Wuxi to the east, Xuancheng (Anhui) to the south, and Nanjing to the west.
Document 9: Tongzhou District, Nantong: Tongzhou District (Chinese:  通州區 ,  通州区 ,  "Tōngzhōu Qū"), formerly Tongzhou City, is one of three urban districts of Nantong in eastern China's Jiangsu province. It was a county-level city under the administration of Nantong until 2010, when it became a district of Nantong. As of 2010, Tongzhou had a population of 1,246,400.
Document 10: Xiaogan: Xiaogan () is a prefecture-level city in east-central Hubei province, People's Republic of China, some 60 km northwest of the provincial capital of Wuhan. According to the 2010 census, its population totaled 4,814,542, of whom 908,266 lived in the built-up ("or metro") area of Xiaonan District.
Document 11: Gao'an: Gao'an () is a city in the province of Jiangxi, China. It is a county-level city, under the jurisdiction of the prefecture-level city of Yichun.
Document 12: Zhuzhou: Zhuzhou (), formerly Jianning, is a prefecture-level city of Hunan Province, China, a little to the southeast of Changsha and bordering Jiangxi to the east. It is part of the "ChangZhuTan Golden Triangle" (comprising the cities of Changsha, Zhuzhou and Xiangtan). The city has jurisdiction over 5 counties (Yanling, Chaling, Youxian, Liling, Zhuzhou) and four districts (Hetang, Lusong, Shifeng and Tianyuan, a high-tech industrial development zone), and covers an area of 11420 km2 .
Document 13: Ruijin: Ruijin () is a county-level city of Ganzhou in the mountains bordering Fujian Province in south-eastern Jiangxi.
Document 14: Gaozhou: Gaozhou is a county-level city in southwestern Guangdong Province, China. Formerly the primary city in the area, it is now administered as part of the prefecture-level city of Maoming. At the time of the 2010 census, Gaozhou had a population of 1,288,665 living in its 3270.8 sqkm territory. The locals speak a variation of the Gaozhou dialect. It is best known in China for being the ancestral home of Leo Ku.
Document 15: Zhangjiagang: Zhangjiagang (), formerly Shazhou County (沙洲县), is a county-level city under the administration of Suzhou, Jiangsu province, China. With 1,246,762 inhabitants at the 2010 census, the city is now part of Jiangyn-Zhangjiagang-Jingjiang metropolitan area with 3,526,260 inhabitants. Continued growth will encompass the Shanghai-Suzhou-Wuxi-Changzhou Metroplex. It borders the prefecture-level cities of Taizhou and Nantong across the Yangtze River, as well as Wuxi to the west.
ground_truth: Zhangjiagang