Option (C) is correct. According to the textbook context, sodium bicarbonate is added to animal cell culture media to maintain the correct pH when CO₂ is present. The context explains that bicarbonate buffering follows Le Chatelier's principle - when acidity increases due to H⁺ ions, free bicarbonate ions react with the extra H⁺ ions to form carbonic acid, stabilizing the pH. The text specifically states that 'Stabilisation of pH over a range of % CO₂ can be achieved using an appropriate HCO₃⁻ concentration.' This confirms that sodium bicarbonate works in conjunction with CO₂ to maintain proper pH levels in the culture medium, which is essential for optimal cell growth.