口服制酸懸液劑配方如下，其中glycerin最可能扮演何種角色？ aluminum hydroxide compressed gel 163.4 g sorbitol solution 141.0 mL syrup 46.5 mL glycerol 12.5 mL methylparaben 0.45 g propylparaben 0.15 g flavor qs purified water, to make 500.0 mL