The correct answer is: A. carbonic acid.
Carbonic acid is a weak acid that is formed when carbon dioxide dissolves in water. It is the main component of carbonated beverages, such as soda and sparkling water. Carbonic acid gives these beverages their characteristic fizzy taste.
Tartaric acid is a white, crystalline solid that is found in many fruits, such as grapes and raspberries. It is also used as a food additive and in the manufacture of baking powder.
Citric acid is a white, crystalline solid that is found in citrus fruits, such as lemons and limes. It is also used as a food additive and in the manufacture of cleaning products.
Oxalic acid is a white, crystalline solid that is found in many plants, such as spinach and rhubarb. It is also used as a cleaning agent and in the manufacture of dyes.
Carbonic acid is the only one of these acids that is found in soft drinks.