A Study to Evaluate Serplulimab in Combination With Docetaxel +S-1 VS. Docetaxel +S-1 as Adjuvant Treatment Therapy in Stage IIIc Gastric Cancer

Serplulimab, 4.5mg/kg solution intravenously for 30 min in first day every 3 weeks. Repeated every 21 days. 21 days for a cycle.

40 mg/m\^2 solution intravenously for 1 hour in first day every 3 weeks. Repeated every 21 days, 21 days for a cycle, from second cycle to seventh cycle.

Tegafur-gimeracil-oteracil potassium: 50mg bid orally in 14 days, followed by 7 days off. Rrepeated every 21 days. 21 days for a cycle.