Step 1: Understanding the Concept:
Glass transition temperature (Tg) is important for polymers.
Additives can affect Tg.
Step 2: Key Formula or Approach:
No specific formula.
Need to know the effects of additives on Tg.
Step 3: Detailed Explanation:
Plasticizers decrease the glass transition temperature of biopolymers.
They increase flexibility and reduce brittleness.
UV stabilizers, antioxidants, and reinforcing agents do not decrease Tg.
Thus, plasticizers are the correct answer.
Step 4: Final Answer:
Plasticizers decrease the glass transition temperature.
Hence, the correct option is (D).