Ph1b/2 Study of the Safety and Efficacy of SHR-A1811 Combinations in Advanced HER2 Expression Gastric Cancer

(Arm 1A) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1701, administered as an IV infusion;

(Arm 1B) Drug: SHR-A1811, administered as an IV infusion Drug：capecitabine, administered orally；

(Arm 1C) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1701, administered as an IV infusion Drug：capecitabine, administered orally；

(Arm 1D) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316, administered as an IV infusion Drug：capecitabine, administered orally；

(Arm 1F) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316, administered as an IV infusion Drug：capecitabine, administered orally； Drug：oxaliplatin，administered as an IV infusion

(Arm 1G) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316, administered as an IV infusion Drug：5-FU，administered as an IV infusion

(Arm 2A) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316 administered as an IV infusion; Drug：capecitabine, administered orally；

(Arm 2B) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316, administered as an IV infusion

(Arm 2C) Drug: SHR-A1811, administered as an IV infusion Drug：capecitabine, administered orally；

(Arm 2D) Drug: SHR-A1811, administered as an IV infusion Drug: SHR-1316, administered as an IV infusion Drug：5-FU，administered as an IV infusion

(Arm 2E) Drug: SHR-A1811, administered as an IV infusion Drug：5-FU，administered as an IV infusion

(Arm 2F) Drug: SHR-A1811,administered as an IV infusion Drug: SHR-1316, administered as an IV infusion Drug：capecitabine, administered orally； Drug：oxaliplatin，administered as an IV infusion